problem closing workbooks

When I try to close a workbook ..
Instead of closing the spreadsheet file immediately, the
mouse converts to an hourglass and the taskbar opens up
another excel icon. Excel then hangs until the file
closes. Sometimes this can take several minutes and
virtually locks Excel whilst this is occurring.

I am using XP professional and am connected to an NT
network. other users on the system have complained of the
same problem. Is this a network error?