I have developed an application in Excel 2000 (SP3) for a colleague using
2003. The main bulk of the application is moving data around, although there
is some charting.

When my colleague tries to open the workbook he gets the usual secuirty
warning about opening the book with the macros in and then gets an error
message saying that Excel has encountered a problem and has to close. If you
reopen it Excel tries to 'repair' the problem by removing the VBA.

Is this a compatibility issue?

Thanks,
Ben