I have an Excel spreadsheet that randomly pops up with a Microsoft
Visual Basic Error:

Class not registered.
Looking for object with CLSID:{AC9F2F90-E877-11CE-9F68-00AA00574A4F}

I've checked the Microsoft knowledge base and found this article
http://support.microsoft.com/kb/182500/en-us, and found that re-
registering FM20.dll fixes the issue. I un-register and re-register C:
\Windows\System32\FM20.dll and this fixes the issue. Unfortunately,
the error re-appears randomly.

Does anyone know what will cause FM20.dll to become corrupt and
require re-registering?

Any help will be greatly appreciated.

Steve