illegal operation opening a shared Excel workbook

[BG250]

Microsoft Office 2000 service pack 3
Windows 2000 service pack 4
File resides on the server drive. Some users get the error when they try to
open the file. Others can open the file without error. I can open the file,
turn off the sharing, save the file and exit. Now that user can open the
file without error. If they enable sharing again, this problem may affect
another user.
I checked the MS knowledgebase and found nothing significant relating to
this problem.
Any ideas?

Thanks bg