Explorer.exe Hangs On Shutdown?

One of the computers in the office where I work hangs when the user shuts down in the evening. The error dialog says there are two processes still running, and the title bar of the dialog says "explorer.exe error". The message in the dialog says something like "The instruction at "0xXXXXXXXX" referenced memory at "0xXXXXXXXX", The memory could not be "written. Click OK to close." There is an OK button and when you click it, the computers finishes it's shutdown with no further hang up. Windows explorer is the stuck process shown. I've done a little research on it and some of the suggestions are to clear the temporary internet files, which I did, but that didn't help and I wonder if they were thinking IE and not the Windows explorer which is different.