Hope someone can help with this problem...

I have an Excel worksheet that is using a few combo boxes.
If you pick a value from any of the combo boxes and then move
the focus to another cell or combo box using the mouse, life is good.

But if you dare use the TAB or ENTER keys to move the focus,
Excel crashes.

Has anyone encountered this problem? It happens whether the sheet
is protected or not. It happens is Excel 2003, XP, or 2000 (in 97, the
focus
just seems to get lost, but I don't care as I do not need it to work in
97).
It happens whether the AutoTab property is set to True or False.

I am stumped...