Invalid page fault in module Excel.exe

I have an excel workbook file on my server that is used by different people. When I go in a review a work sheet and exit it cannot be accessed by other people and sometimes it lets them open it in read only. When they get the message that it can beopened in read only it states that the file is being edited by me, but I have closed the file and not using it. Is this a problem caused by the network or is it an application problem. Also I use Excel 2000 and some of the others use Excel 97. CanI stop this from happening?

Thanks,

John Starnes