Yes... the problem is when you actually CLOSE the workbook, not when
you just have only hidden sheets in a still open workbook . The VBE
actually shows the same phantom workbook name over and over in the VBE
(which shouldn't even be possible). And as mentioned, you can edit
any of the phantoms and completely waste your time since there's no
way to save the phantoms. It is some sort of resource release problem
as Jon mentions.

Jon, what is a "COM" add-in? I don't have any special add-ins from
the Tools - Add-ins menu or in the Add-in Manager in the VBE. Is
there somewhere else to check? How do I uninstall a COM add-in?

I have one unique add-in called "XLFit", but I don't see where that is
being loaded. It checks for certain formulas in a spreadsheet, and if
detected, it then loads the main mother add-in to provide
functionality. The main add-in is an extremely complex charting macro
which sounds like may be similar to the Sparkline chart tools (??).

Thanks for your help! This problem is a big hassle when testing and
would be great to figure out.

John