Shared excel file dissapears

[Cnews-ms]

We use a shared excel 2000 xls file shared on a w2k server as a production
log. we now have about 30 users with about 12 users constantly editing. As
we add more users the dissapearances seem to mount up. we are at about 2 a
day now.
I was wondering what the max amount vs the recommended amount of
simultaneous users are. Are there any known issues which would cause excel
to mysteriously vanish??

thanks

cr