NullReferenceException error on Play in IDE

I get the following error whenever I simply click play in the editor. The problem seems to be pointing to a problem within the editor itself. The issue is identical using both Unity 4.5.4 and Unity 4.6 beta17 on Windows 8.1. Can any Unity experts suggest some troubleshooting steps?

NullReferenceException: Object
reference not set to an instance of an
UnityEditor.DockArea.OnGUI () (at C:/BuildAgent/work/d63dfc6385190b60/Editor/Mono/GUI/DockArea.cs:598)

Thanks @Smoggach -

resetting the layout to default, and maybe a few restarts, seems to fix this latest ridiculous fuckup by Unity.

Thanks for that.