MissingMethodException:

Are you seeing this error when you load a blank Unity project, or does it only happen in one of your current projects? If the former, you should submit a bug report directly to Unity, which you can do from the editor application or the bug reporter application (installed with Unity).

Does AppStatusBar inherit from a class that defines OnGUI? If yes, is it abstract or virtual? Are you overriding it in AppStatusBar?

@$$anonymous$$ortoc, The reason I ask about the editor is this forum post, that seems to be the same issue:

http://forum.unity3d.com/threads/141763-Unity3D-AppStatusBar-Error

And again on this site:

http://answers.unity3d.com/questions/259020/unity-35-erros.html

It seems to be an ongoing issue, and I'm curious whether it's something in the Unity Editor or perhaps an issue with a common Asset Store item like EZGUI.