Macro no longer works now that in Excel XP

[C.B.]

Now that I have upgraded to Office XP, a macro in one
existing file no longer works. It worked fine in Excel
2000. The macro was probably created in Excel 97.

Macros created in other workbooks work just fine in Excel
XP. But any macro created in that specific existing
workbook do not work. The workbook has protection on it,
but it is disabled when I enter the password at open time.

What's up? Macro security is set to Medium.

Thanks