UPDATE ......From Tuesday 8 April 2025 we have changed the way that Single Sign-on works on this wiki. Please see here for more information:
Update
This error was popping up on a Windows 7 64 box with Office 2007 installed, after MS12-027 was applied.
After looking at http://www.lessanvaezi.com/delete-exd-files-to-fix-object-library-invalid-error/ and removed the EXD files things magically started working again...