Visual Basic Editor opens bi itself
 

I believe that I saw something about this a long time ago but I can't seem to
locate it.

I have a workbook (Excel 2002) that contains VBA code. When the workbook is
open and the PC has been idle for a while, I return to find that, all by
itself, Excel has opened and is displaying the Visual Basic Editor window. I
don't want to hand the workbook over to the ultimate user with this glitch
because it will confuse the heck out of them.

Any ideas what is causing this and how to prevent it?