I have a problem with my Unity editor!

I might have problem with my Unity editor. when i import a package such as ''Standard Assets"
I get a ton of errors like:" UnityEditor.BuildTargetGroup.PSM is obsolete."
"UnityEngine.GUIText' is obsolete"
"UnityEngine.Object.DestroyObject(UnityEngine.Object)' is obsolete"
"UnityEngine.GUITexture' is obsolete"
"UnityEngine.Object.DestroyObject(UnityEngine.Object)' is obsolete"

I have a critical error as well:
PlayerSettings Validation: Requested build target group (20) doesn't exist; #define symbols for scripting won't be added.
UnityEditor.PlayerSettings:SetScriptingDefineSymbolsForGroup(BuildTargetGroup, String)
UnityStandardAssets.CrossPlatformInput.Inspector.CrossPlatformInitialize:SetEnabled(String, Boolean, Boolean) (at Assets/Standard Assets/Editor/CrossPlatformInput/CrossPlatformInputInitialize.cs:127)
UnityStandardAssets.CrossPlatformInput.Inspector.CrossPlatformInitialize:.cctor() (at Assets/Standard Assets/Editor/CrossPlatformInput/CrossPlatformInputInitialize.cs:22)
UnityEditor.EditorAssembliesrocessInitializeOnLoadAttributes()

I don't know what to do. does this have to do something with my VisualStudio?
need help...

 

As far as I know these errors are because some of these build targets where removed since the Unity version those Standard Assets were last added/modified.

Me myself have found that error message for the "build target group (20)" too (at least in 2018.1.6f1-2018.1.8f1). It should not be something to worry about (i.e. ignore them), but if you don't want to see them popping again, go and open:

<ProjectFolder>\Assets\Standard Assets\Editor\CrossPlatformInput\CrossPlatformInputInitialize.cs

And delete the lines with references to

BuildTargetGroup.PSM

, at least the error has not appeared to me again since then.

 

Thanks were effective