Question Error: The reference assemblies for .NETFramework,Version=v4.7.1 were not found

Hello everyone,
My Unity project was working great yesterday but today it start throwing some errors and problems. I did't change anything today. But Visual Studio Code was updating Omnisharp etc in the morning. I am not sure what is the main cause of problems. I am getting this error in Unity Console:

Code (CSharp):

1. ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
2. Parameter name: index
3. System.ThrowHelper.ThrowArgumentOutOfRangeException (System.ExceptionArgument argument, System.ExceptionResource resource) (at <fb001e01371b4adca20013e0ac763896>:0)
4. System.ThrowHelper.ThrowArgumentOutOfRangeException () (at <fb001e01371b4adca20013e0ac763896>:0)
5. System.Collections.Generic.List`1[T].get_Item (System.Int32 index) (at <fb001e01371b4adca20013e0ac763896>:0)
6. CarSelection.LoadNewCar (System.Int32 playerNumber) (at D:/Unity Backups/Backup 41 Built in Pipeleine/Mini Racer Xtreme 5 Built In Pipeline/Assets/MCR Creator/Assets/Scripts/Menu/CarSelection.cs:291)
7. CarSelection.initCarSelection (System.Int32 NumberOfPlayer) (at D:/Unity Backups/Backup 41 Built in Pipeleine/Mini Racer Xtreme 5 Built In Pipeline/Assets/MCR Creator/Assets/Scripts/Menu/CarSelection.cs:243)
8. UnityEngine.Events.InvokableCall`1[T1].Invoke (T1 args0) (at <a979f18d51af41179d12b797e8c5be14>:0)
9. UnityEngine.Events.CachedInvokableCall`1[T].Invoke (System.Object[] args) (at <a979f18d51af41179d12b797e8c5be14>:0)
10. UnityEngine.Events.UnityEvent.Invoke () (at <a979f18d51af41179d12b797e8c5be14>:0)
11. UnityEngine.UI.Button.Press () (at C:/Program Files/2019.4.6f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/UI/Core/Button.cs:68)
12. UnityEngine.UI.Button.OnPointerClick (UnityEngine.EventSystems.PointerEventData eventData) (at C:/Program Files/2019.4.6f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/UI/Core/Button.cs:110)
13. UnityEngine.EventSystems.ExecuteEvents.Execute (UnityEngine.EventSystems.IPointerClickHandler handler, UnityEngine.EventSystems.BaseEventData eventData) (at C:/Program Files/2019.4.6f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/EventSystem/ExecuteEvents.cs:50)
14. UnityEngine.EventSystems.ExecuteEvents.Execute[T] (UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.ExecuteEvents+EventFunction`1[T1] functor) (at C:/Program Files/2019.4.6f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/EventSystem/ExecuteEvents.cs:261)
15. UnityEngine.EventSystems.EventSystem:Update() (at C:/Program Files/2019.4.6f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/EventSystem/EventSystem.cs:377)
16.  

And these errors in Visual Studio Code:

Code (CSharp):

1. Starting OmniSharp server at 8/17/2020, 9:55:37 PM
2.     Target: d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Mini Racer Xtreme 3.sln
3.  
4. OmniSharp server started.
5.     Path: c:\Users\Hi\.vscode\extensions\ms-dotnettools.csharp-1.23.0\.omnisharp\1.36.1\OmniSharp.exe
6.     PID: 7056
7.  
8. [info]: OmniSharp.Stdio.Host
9.         Starting OmniSharp on Windows 6.2.9200.0 (x64)
10. [info]: OmniSharp.Services.DotNetCliService
11.         DotNetPath set to dotnet
12. [info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
13.         Located 1 MSBuild instance(s)
14.             1: StandAlone 16.8.0 - "c:\Users\Hi\.vscode\extensions\ms-dotnettools.csharp-1.23.0\.omnisharp\1.36.1\.msbuild\Current\Bin"
15. [info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
16.         MSBUILD_EXE_PATH environment variable set to 'c:\Users\Hi\.vscode\extensions\ms-dotnettools.csharp-1.23.0\.omnisharp\1.36.1\.msbuild\Current\Bin\MSBuild.exe'
17. [info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
18.         Registered MSBuild instance: StandAlone 16.8.0 - "c:\Users\Hi\.vscode\extensions\ms-dotnettools.csharp-1.23.0\.omnisharp\1.36.1\.msbuild\Current\Bin"
19.             CscToolExe = csc.exe
20.             CscToolPath = c:\Users\Hi\.vscode\extensions\ms-dotnettools.csharp-1.23.0\.omnisharp\1.36.1\.msbuild\Current\Bin\Roslyn
21.             MSBuildExtensionsPath = c:\Users\Hi\.vscode\extensions\ms-dotnettools.csharp-1.23.0\.omnisharp\1.36.1\.msbuild
22.             MSBuildToolsPath = c:\Users\Hi\.vscode\extensions\ms-dotnettools.csharp-1.23.0\.omnisharp\1.36.1\.msbuild\Current\Bin
23. [info]: OmniSharp.Cake.CakeProjectSystem
24.         Detecting Cake files in 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline'.
25. [info]: OmniSharp.Cake.CakeProjectSystem
26.         Could not find any Cake files
27. [info]: OmniSharp.MSBuild.ProjectSystem
28.         Detecting projects in 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Mini Racer Xtreme 3.sln'.
29. [info]: OmniSharp.MSBuild.ProjectManager
30.         Queue project update for 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp.csproj'
31. [info]: OmniSharp.MSBuild.ProjectManager
32.         Queue project update for 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\GoogleMobileAds.csproj'
33. [info]: OmniSharp.MSBuild.ProjectManager
34.         Queue project update for 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-firstpass.csproj'
35. [info]: OmniSharp.MSBuild.ProjectManager
36.         Queue project update for 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-Editor-firstpass.csproj'
37. [info]: OmniSharp.MSBuild.ProjectManager
38.         Queue project update for 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\GoogleMobileAds.Editor.csproj'
39. [info]: OmniSharp.MSBuild.ProjectManager
40.         Queue project update for 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-Editor.csproj'
41. [info]: OmniSharp.Script.ScriptProjectSystem
42.         Detecting CSX files in 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline'.
43. [info]: OmniSharp.MSBuild.ProjectManager
44.         Loading project: d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp.csproj
45. [info]: OmniSharp.Script.ScriptProjectSystem
46.         Could not find any CSX files
47. [info]: OmniSharp.WorkspaceInitializer
48.         Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpFormattingWorkspaceOptionsProvider, Order: 0
49. [info]: OmniSharp.WorkspaceInitializer
50.         Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.RenameWorkspaceOptionsProvider, Order: 100
51. [info]: OmniSharp.WorkspaceInitializer
52.         Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.ImplementTypeWorkspaceOptionsProvider, Order: 110
53. [info]: OmniSharp.WorkspaceInitializer
54.         Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.BlockStructureWorkspaceOptionsProvider, Order: 140
55. [info]: OmniSharp.WorkspaceInitializer
56.         Configuration finished.
57. [info]: OmniSharp.Stdio.Host
58.         Omnisharp server running using Stdio at location 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline' on host 11288.
59. [fail]: OmniSharp.MSBuild.ProjectLoader
60.         The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks
61. [warn]: OmniSharp.MSBuild.ProjectManager
62.         Failed to load project file 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp.csproj'.
63. d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp.csproj
64. c:\Users\Hi\.vscode\extensions\ms-dotnettools.csharp-1.23.0\.omnisharp\1.36.1\.msbuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(1178,5): Error: The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks
65.  
66. [info]: OmniSharp.MSBuild.ProjectManager
67.         Loading project: d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\GoogleMobileAds.csproj
68. [fail]: OmniSharp.MSBuild.ProjectLoader
69.         The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks
70. [warn]: OmniSharp.MSBuild.ProjectManager
71.         Failed to load project file 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\GoogleMobileAds.csproj'.
72. d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\GoogleMobileAds.csproj
73. c:\Users\Hi\.vscode\extensions\ms-dotnettools.csharp-1.23.0\.omnisharp\1.36.1\.msbuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(1178,5): Error: The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks
74.  
75. [info]: OmniSharp.MSBuild.ProjectManager
76.         Loading project: d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-firstpass.csproj
77. [fail]: OmniSharp.MSBuild.ProjectLoader
78.         The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks
79. [warn]: OmniSharp.MSBuild.ProjectManager
80.         Failed to load project file 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-firstpass.csproj'.
81. d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-firstpass.csproj
82. c:\Users\Hi\.vscode\extensions\ms-dotnettools.csharp-1.23.0\.omnisharp\1.36.1\.msbuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(1178,5): Error: The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks
83.  
84. [info]: OmniSharp.MSBuild.ProjectManager
85.         Loading project: d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-Editor-firstpass.csproj
86. [fail]: OmniSharp.MSBuild.ProjectLoader
87.         The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks
88. [warn]: OmniSharp.MSBuild.ProjectManager
89.         Failed to load project file 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-Editor-firstpass.csproj'.
90. d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-Editor-firstpass.csproj
91. c:\Users\Hi\.vscode\extensions\ms-dotnettools.csharp-1.23.0\.omnisharp\1.36.1\.msbuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(1178,5): Error: The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks
92.  
93. [info]: OmniSharp.MSBuild.ProjectManager
94.         Loading project: d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\GoogleMobileAds.Editor.csproj
95. [fail]: OmniSharp.MSBuild.ProjectLoader
96.         The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks
97. [warn]: OmniSharp.MSBuild.ProjectManager
98.         Failed to load project file 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\GoogleMobileAds.Editor.csproj'.
99. d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\GoogleMobileAds.Editor.csproj
100. c:\Users\Hi\.vscode\extensions\ms-dotnettools.csharp-1.23.0\.omnisharp\1.36.1\.msbuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(1178,5): Error: The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks
101.  
102. [info]: OmniSharp.MSBuild.ProjectManager
103.         Loading project: d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-Editor.csproj
104. [fail]: OmniSharp.MSBuild.ProjectLoader
105.         The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks
106. [warn]: OmniSharp.MSBuild.ProjectManager
107.         Failed to load project file 'd:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-Editor.csproj'.
108. d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-Editor.csproj
109. c:\Users\Hi\.vscode\extensions\ms-dotnettools.csharp-1.23.0\.omnisharp\1.36.1\.msbuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(1178,5): Error: The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks
110.  
111. [fail]: OmniSharp.MSBuild.ProjectManager
112.         Attempted to update project that is not loaded: d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp.csproj
113. [fail]: OmniSharp.MSBuild.ProjectManager
114.         Attempted to update project that is not loaded: d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\GoogleMobileAds.csproj
115. [fail]: OmniSharp.MSBuild.ProjectManager
116.         Attempted to update project that is not loaded: d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-firstpass.csproj
117. [fail]: OmniSharp.MSBuild.ProjectManager
118.         Attempted to update project that is not loaded: d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-Editor-firstpass.csproj
119. [fail]: OmniSharp.MSBuild.ProjectManager
120.         Attempted to update project that is not loaded: d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\GoogleMobileAds.Editor.csproj
121. [fail]: OmniSharp.MSBuild.ProjectManager
122.         Attempted to update project that is not loaded: d:\Unity Backups\Backup 43 Built\Mini Racer Xtreme 7 Built In Pipeline\Assembly-CSharp-Editor.csproj
123.  

While i have the latest NET Framework v4.8 installed already.
I also tried with some old backups of this project but I am getting same errors.

 

Problem is Solved Now.

 

Mind sharing what your solution was?

 

Actually it's related to an asset downloaded from Unity Asset Store. When I fixed that, It removed error in Unity Console. And Visual Code error not matter for me as long as everything is working fine.

 

Hi !

I have the same issue on Linux, getting this error message :

The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks

The problem is that I can't find the Developer Packs for linux, only a Windows version seems available :/

What could I do ?