I previously had a problem where my VBA macro was hacked away at my User and System resources.

I managed to "solve" the problem by using the DoEvents command.

Basically, DoEvents momentarily releases control to the OS, so as to allow it to "catch-up" and/or perform other various events which might be necessary for the VBA to complete. (for example, Serial/parrallel port communication, etc).

There is more information on it in the Microsoft Knowledge Base, I just don't have the article number with me right now.

Hope someone else also finds this useful!