Do you have any macros running (even events _activate and _deactivate (workbook
or worksheet)))?

If you close excel and reopen in safe mode (which will disable all macros), does
it work?

close excel
windows start button|run
excel /safe

file|Open both workbooks.



Michael Malinsky wrote:

I switch between the workbooks using either the taskbar or Alt+Tab. I
have no keyboard shortcuts at all.

--

Dave Peterson