Excel 2007 - only administrators can open files read-only

[bartlettit]

When files are already open by another user, we have found that only
users with Administrator permissions on their computers are able to
open files read-only. If the user only has basic user permissions
they receive a message stating the file could not be found.

This was not a problem with Office 2000 (which we recently upgraded
from).

Any ideas?

Thanks,

Chris