Did you try this?

On the server, right-click on My Computer, then select Manage, expand Shared
Folders, and click on Open Files. There you'll see a list of files on the
server that are currently opened by other computers on your network. That'll
tell you the User who has the file open. You'll need to then click on
Sessions to see what computer(s) that user is connecting from.

"Todd Virlee" wrote:

We have a VB 6 program that one of the things that it does is open
spreadsheets as Excel.Application's, but a client of ours gets a message that
the files are in use. The files are not in use. All users have rebooted
their machines. This started occurring after they did an upgrade to Office
2003.

Other clients do not have this problem. Is there a setting that could have
been changed during this upgrade?