AutoNumber field problems in Access97

Occationally we have problems with “missing” numbers in an auto number field. I am the only one that has permission to delete records from this table, so I know that is not the reason for these missing numbers, as I’ve not deleted any records.
The database is on a server that occationally has problems, but that shouldn’t create skipped numbers, or could it somehow?
I can’t think of any logical explanations, and the missing numbers generate “problems” in record keeping.
1. What could be causing this?
2. How can I prevent this problem in the future?
Thank you