PrecompiledAssemblyException: Multiple precompiled assemblies with the same name Mono.Cecil.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.IEnumerable1[T] customScriptAssemblies, System.Collections.Generic.IEnumerable1[T] precompiledAssemblies) (at D:/unity/Editor/Mono/Scripting/ScriptCompilation/EditorBuildRules.cs:221)
UnityEditor.Scripting.ScriptCompilation.EditorCompilation.UpdateCustomTargetAssemblies () (at D:/unity/Editor/Mono/Scripting/ScriptCompilation/EditorCompilation.cs:672)
UnityEditor.Scripting.ScriptCompilation.EditorCompilation.SetAllCustomScriptAssemblyJsonContents (System.String[] paths, System.String[] contents, System.String[] guids) (at D:/unity/Editor/Mono/Scripting/ScriptCompilation/EditorCompilation.cs:892)
UnityEditor.Scripting.ScriptCompilation.EditorCompilationInterface.SetAllCustomScriptAssemblyJsonContents (System.String[] allAssemblyJsonPaths, System.String[] allAssemblyJsonContents, System.String[] guids) (at D:/unity/Editor/Mono/Scripting/ScriptCompilation/EditorCompilationInterface.cs:241)

解決方案如下

1：打開packages manager ，在window->packages Manager。然后把能升級(jí)的package 都升級(jí)了。應(yīng)該就解決了

如果找不到Packages Manager
2: (1) 打開項(xiàng)目目錄下的 Logs->Packages-Update.log。 看看都更新了什么package。
(2) 打開項(xiàng)目目錄下的Packages->manifest.json。 備份里面的內(nèi)容，然后刪除unity升級(jí)時(shí)加的package。
(3)重啟unity，這個(gè)時(shí)候錯(cuò)誤應(yīng)該消失了。
(4)打開packages manager ，在window->packages Manager。然后把能升級(jí)的package 都升級(jí)了。
(5)把第二部刪除的package添加回來
(6)重啟unity