First I would pack and reindex the serialno_table.
Then I would review the code to see whether code is looking into actual table, or into the view that was created upon form opening (and in this case the view should be refreshed before assigning the new serialno).

>I have written an application which uses many different forms. One part of the application adds a record into a table, and assigns that record a 'serial number'. The last serial number used is held in a separate table called serialno. When the application adds a record, it adds 1 to the serial number in store (ie serialno.nlastSN = serialno.nlastSN + 1).
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>This is a multiuser application. For some reason, all of a sudden, when one of the other users enters a record, the application picks up serialno.nlastSN about three numbers back. Is this something to do with data sessions? How do I check? It seems to happen kinda randomly.....
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>CM