求助 这是那里出了问题？

System.TypeInitializationException: The type initializer for 'Boo.Lang.Compiler.TypeSystem.Types' threw an exception. ---> System.TypeLoadException: Could not load type 'System.Runtime.CompilerServices.ExtensionAttribute' from assembly 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.
at Boo.Lang.Compiler.TypeSystem.Types..cctor()
--- End of inner exception stack trace ---
at Boo.Lang.Compiler.TypeSystem.Reflection.ReflectionTypeSystemProvider.ObjectTypeImpl..ctor(IReflectionTypeSystemProvider provider)
at Boo.Lang.Compiler.TypeSystem.Reflection.ReflectionTypeSystemProvider..ctor()
at UnityScript.UnityScriptCompilerParameters..ctor(Boolean loadDefaultReferences)
at UnityScript.UnityScriptCompilerParameters..ctor()
at UnityScript.UnityScriptCompiler..ctor()
at UnityScript.MonoDevelop.ProjectModel.UnityScriptParserModule.ParseUnityScript(String fileName, String content)
at UnityScript.MonoDevelop.ProjectModel.UnityScriptParser.Parse(Boolean storeAst, String fileName, TextReader reader, Project project)
at MonoDevelop.SourceEditor.SourceEditorView.RunFirstTimeFoldUpdate(String text) in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\src\addins\MonoDevelop.SourceEditor2\MonoDevelop.SourceEditor\SourceEditorView.cs:line 734
at MonoDevelop.SourceEditor.SourceEditorView.Load(String fileName, Encoding loadEncoding) in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\src\addins\MonoDevelop.SourceEditor2\MonoDevelop.SourceEditor\SourceEditorView.cs:line 819
at MonoDevelop.SourceEditor.SourceEditorView.Load(String fileName) in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\src\addins\MonoDevelop.SourceEditor2\MonoDevelop.SourceEditor\SourceEditorView.cs:line 729
at MonoDevelop.Ide.Gui.LoadFileWrapper.Invoke(String fileName) in c:\BuildAgent\work\d478831d940d36a4\monodevelop\main\src\core\MonoDevelop.Ide\MonoDevelop.Ide.Gui\Workbench.cs:line 1201

没救了吗？