appointments multiplying

I keep our company appointment calendar on Outlook 2000
and share the document with nine other computers. Updates
flow from the master file to the other computers and most
of the computers are listed as editors so their additions
and changes flow back to the master file. we archive and
clean out the file very month to control the number of
appointments listed. The problem is that from time to time
when you enter an appointment it multiplies itself and can
be copied on the same line six to ten times.

I'm lost, can you help?