I've created an ActiveX control and compiled it as an OCX.

If I then add the control to an Excel spreadsheet it will
sometimes cause excel to crash.  The crash can occur
straight away on opening the file or may happen after a
while or sometimes only when when you close Excel.

This only happens in XP or 2000 and only on a majority
rather than all machines.  There were no problems in
office 97.

Generally either no specific error message is received
but on one machine the following appeared:

The instruction at 0x77f537fe referenced memory at
0xfffffff8. The memory could not be read.

any thoughts on the best way to find the problem or what
it might be?

Thanks

Duncan