Эта ошибка возникает в Build даже при пустом проекте:
ArgumentException: The Assembly UnityEditor is referenced by UnityEngine.UI ('F:/Program Files/Unity/Editor/Data/UnityExtensions/Unity/GUISystem/Standalone/UnityEngine.UI.dll'). But the dll is not allowed to be included or could not be found.
UnityEditor.AssemblyHelper.AddReferencedAssembliesRecurse (System.String assemblyPath, System.Collections.Generic.List`1[T] alreadyFoundAssemblies, System.String[] allAssemblyPaths, System.String[] foldersToSearch, System.Collections.Generic.Dictionary`2[TKey,TValue] cache, UnityEditor.BuildTarget target) (at C:/buildslave/unity/build/Editor/Mono/AssemblyHelper.cs:150)
UnityEditor.AssemblyHelper.AddReferencedAssembliesRecurse (System.String assemblyPath, System.Collections.Generic.List`1[T] alreadyFoundAssemblies, System.String[] allAssemblyPaths, System.String[] foldersToSearch, System.Collections.Generic.Dictionary`2[TKey,TValue] cache, UnityEditor.BuildTarget target) (at C:/buildslave/unity/build/Editor/Mono/AssemblyHelper.cs:156)
UnityEditor.AssemblyHelper.FindAssembliesReferencedBy (System.String[] paths, System.String[] foldersToSearch, UnityEditor.BuildTarget target) (at C:/buildslave/unity/build/Editor/Mono/AssemblyHelper.cs:190)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)
Я пытался изменить уровень совместимости Api, как предлагалось на некоторых форумах, и возникал вопрос о переполнении стека, но, похоже, ничего не работает.