A local computer consulting client started getting this error every time she tried to close Word or Excel:

The instruction at “0x01003ce4” referenced memory at “0x00000018”.  The memory could not be “read”.  Click on OK to terminate.  Click Cancel to debug the program.

I did a quick search and only saw errors about Office Live Sign in and thought that couldn't be it.  I went on site to remove and reinstall Office.  I first reproduced the error and saw that the message box had "OfficeLiveSignIn.exe - Application Error." in the heading.  The user was using the Office Live messenger instant messaging client.  It had installed an addon to Word and Excel.  Disabling this addon fixed the problem.