I have created an Excel add-in using Visual C++. It works
great on Windows 95/98/Me with several versions of Excel.
When I use it on Windows XP and Windows 2000, the add-in
will load, but then if I close Excel and try to come back
in, I get an error message that the addin is not a
recognizable format. Every time I go into Excel I have to
go to Tools/Add-in and put the add-in back in. Then it
works fine.

For Windows XP, I found a fix. I had to put a few
Microsoft DLLs on the machine and it works great. I had
to put MFC42.dll and MSVCRT.dll in the System folder.
This fix doesn't work for Windows 2000 because there are
newer versions of the DLLs already there.

Any ideas???