2018.3 PrecompiledAssemblyException: Multiple precompiled assemblies with the same name

Hello there,
I tried to upgrade from 2018.2.20 to 2018.3 today and I keep getting this error. Initially there were more but after Reimporting all assets and later deleting the Library folder I could get rid of them. This one is the only one that sticks. I'm not very familiar with assemblies in Unity so any help to deal with that would be very welcome!
Thanks.

PrecompiledAssemblyException: Multiple precompiled assemblies with the same name UnityEngine.Advertisements.Editor.dll included for the current platform. Only one assembly with the same name is allowed per platform. Assembly path: {0}
UnityEditor.Scripting.ScriptCompilation.EditorBuildRules.CreateTargetAssemblies (System.Collections.Generic.IEnumerable`1[T] customScriptAssemblies, System.Collections.Generic.IEnumerable`1[T] precompiledAssemblies) (at C:/buildslave/unity/build/Editor/Mono/Scripting/ScriptCompilation/EditorBuildRules.cs:249)
UnityEditor.Scripting.ScriptCompilation.EditorCompilation.UpdateCustomTargetAssemblies () (at C:/buildslave/unity/build/Editor/Mono/Scripting/ScriptCompilation/EditorCompilation.cs:619)
UnityEditor.Scripting.ScriptCompilation.EditorCompilation.SetAllCustomScriptAssemblyJsons (System.String[] paths) (at C:/buildslave/unity/build/Editor/Mono/Scripting/ScriptCompilation/EditorCompilation.cs:728)
UnityEditor.Scripting.ScriptCompilation.EditorCompilationInterface.SetAllCustomScriptAssemblyJsons (System.String[] allAssemblyJsons) (at C:/buildslave/unity/build/Editor/Mono/Scripting/ScriptCompilation/EditorCompilationInterface.cs:217)

 

Had the same error message, also in 2018.3. Except I got mine from importing a package from one project to another. The project already had Unity Monetization 3.0 built in to it. Not quite sure what I need to fix here to make this work, but I'm going to try commenting out all of the ad code, re-import monetization 3.0 and see if that works. Were you using the monetization asset or just the standard Unity advertisement package?

Update: Upon further investigation, it seems the error is completely linked to a Unity Monetization 3.0 error. I am also getting the following error message 3 times along with the other error message.

Microsoft (R) Visual C# Compiler version 2.9.1.65535 (9d34608e)
Copyright (C) Microsoft Corporation. All rights reserved.

error CS1704: An assembly with the same simple name 'UnityEngine.Advertisements.Editor' has already been imported. Try removing one of the references (e.g. 'C:\Users\userName\Documents\Game Name\Library\PackageCache\com.unity.ads@2.3.1\Runtime\UnityEngine.Advertisements.Editor.dll') or sign them to enable side-by-side.

This seems to offer a solution, but there doesn't seem to be duplicate references in that file location. In my code references, it seem that UnityUngine.Advertisement and UnityEnginge.Advertisement.Editor both have references to Advertisement. I assume one stems from Monitization 3.0 and the other from the Advertisement Package. However, this worked just fine in the project I am importing from. I'll let you know if I figure out the fix.

Fix: This worked for me, but it may not work for you depending on your circumstance, but I simply commented out all references to Advertisement, ie. Advertisement.Show() and Hide(). Went to windows > package manager and removed the advertisement package from the project. Uncommented and the error went away. Hopefully this is helpful to you.

 

I have the same problem with no unity update, tried all solutions, still occurs.

 

Hello. i think i solved this problem in 2 days. In Asset/UnityAds/ i delete those 4 .dll file then my game is working again, the ads is still working fine. tested in android phone

 

For me removing library folder worked, cause it forsed assets reimport.

 

Here is my solution. I had the same error with mono.cecil.dll or something like that.
I search the file in Library\PackageCache found it and delete one of the package containing it (you need to also remove the package from Packages\manifest.json.and it works, Basically I remove t he package that contains it (I need to do this manually because Package manager didn't load because of the error).
It seams to be a problem (at least in my case) with to dlls with the same name in 2 different packages).
Hope this helps.

 

What file did you delete from the Packagecache?

 

I don't remember exactly which one, but you can make a back-up. One was from a package who was in the package manager and the other one was not. I removed the later.
Hope this helps

 

I got the same issue when import the UnityFacebookSDK to project. Turn out there are duplicated libraries, they have two Facebook.Unity.Android.dlls and two Facebook.Unity.IOS.dlls. Here my solution:

• Goto FacebookSDK/Plugins/Android : delete the Facebook.Unity.IOS.dll in that folder
• Goto FacebookSDK/Plugins/IOS : delete the Facebook.Unity.Android.dll
• Exit Unity
• Goto the project Library folder : delete PackageCache and ScriptAssemblies folder
• Restart Unity to let it rebuild the two folders we just delete

It worked for me, hope it'll help you.

 

Thank you so much for the solution ThinhHB, I was having this exact issue after adding FacebookSDK.

 

Worked for me also after installing 2019.1.10f1

 

If you select the .dll file, there is "select platforms for plugin" option in inspector. You probably have the duplicated .dlls aiming same platforms.

So another possible solution:

• Go to FacebookSDK/Plugins/Android : select IOS and Android dlls and choose Android platform.
• Go to FacebookSDK/Plugins/IOS: select IOS and Android dlls and choose IOS platform.

I think this should work.

 

PrecompiledAssemblyException: Multiple precompiled assemblies with the same name UnityEditor.WindowsStandalone.Extensions.dll included for the current platform. Only one assembly with the same name is allowed per platform
C:\Program Files\Unity_2019.3.15f1\Editor\Data\PlaybackEngines\windowsstandalonesupport\UnityEditor.WindowsStandalone.Extensions.dll
C:\Program Files\Unity_2019.3.15f1\Editor\Data\PlaybackEngines\WindowsStandaloneSupport\UnityEditor.WindowsStandalone.Extensions.dll

while checking directory I'm not able to find this directory "C:\Program Files\Unity_2019.3.15f1\Editor\Data\PlaybackEngines\WindowsStandaloneSupport\UnityEditor.WindowsStandalone.Extensions.dll "

do anyone faced this issue in unity 2019?

 

I am not sure about 2019 but I just got this bug in 2018.4 after I enabled In-App Purchasing. Now I cannot see Packager Manager and even resetting project to previous commit does not help. I have to search all places where Unity put their sh... and remove it manually. I hope that will help me get at least project back.

SOLUTION: So I am not 100% sure what was the problem but here is what I did. First I reset all packages to default from Help menu. Then I restarted Unity and imported Firebase packages (analytics, remote config, etc). The restart again and finally removed Fabric folder, since Google no longer support it, the package manager was not able to update it. I waiting for 30 sec while Unity was compiling something and finally Package Manager is back. I hope it will save someone time.

 

It happens to me in 2020.1.7f1 if i solve it i will update

 

In my case it was because I was testing my project on multiple versions of Unity engine (2018, 2019).
I solved it by removing any auto-generated folder by the engine before opening the project

 

PrecompiledAssemblyException: Multiple precompiled assemblies with the same name Google.VersionHandler.dll included for the current platform. Only one assembly with the same name is allowed per platform. Assembly path: {0}
UnityEditor.Scripting.ScriptCompilation.EditorBuildRules.CreateTargetAssemblies (System.Collections.Generic.IEnumerable`1[T] customScriptAssemblies, System.Collections.Generic.IEnumerable`1[T] precompiledAssemblies) (at C:/buildslave/unity/build/Editor/Mono/Scripting/ScriptCompilation/EditorBuildRules.cs:221)
UnityEditor.Scripting.ScriptCompilation.EditorCompilation.UpdateCustomTargetAssemblies () (at C:/buildslave/unity/build/Editor/Mono/Scripting/ScriptCompilation/EditorCompilation.cs:672)
UnityEditor.Scripting.ScriptCompilation.EditorCompilation.SetAllCustomScriptAssemblyJsonContents (System.String[] paths, System.String[] contents, System.String[] guids) (at C:/buildslave/unity/build/Editor/Mono/Scripting/ScriptCompilation/EditorCompilation.cs:892)
UnityEditor.Scripting.ScriptCompilation.EditorCompilationInterface.SetAllCustomScriptAssemblyJsonContents (System.String[] allAssemblyJsonPaths, System.String[] allAssemblyJsonContents, System.String[] guids) (at C:/buildslave/unity/build/Editor/Mono/Scripting/Sc

 

you have files for ios and android on plugins for multi plataforms , you have to uncheck the target plataforms in that file.

 

Same 2021.2.

 

Thanks a lot man that worked for me for another dll with the same issue!

 

I tried your way. Facebook Tabs appear and errors are solved but. URP was deleted. Any methods should I fix ?