Check out the SET DELETED setting. Maybe there are deleted records in a file with the same ID.

>Hello,
>
>I have a "semaphore" file, ReserveGroup.DBF; it has one integer field,
>GROUP, which is also it's primary index, GROUP.
>
>While reservations are being changed in a group, the function LockGroup is
>called; a record in this table is created (if none exists) with the group
>number and the record is locked. Once the reservation changes have been
>completed, the record is unlocked.
>
>Sometimes, the system generates the error "Uniqueness of index GROUP is
>violated" (the error shows in ther error log - 11 times in June, 5 times so
>far in July; different users, different computers). I can't reproduce this
>problem.
>
>ReserveGroup is opened in the Data Environment of the form, w/buffer mode of
>0, and it's order set to GROUP.
>
>This is a peer-to-peer Windows network.
>
>The error occurs at line 10 in the following function...does anyone have any
>suggestions about how to avoid the error?
>
>TIA, J
>
>

** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** **
>** lock GROUP while updating or DELETing
>FUNCTION LockGroup
>
>LPARAMETER nGroupToLock
>
>LOCAL cTheAlias, lLocked
>
>cTheAlias = ALIAS()
>
>SELECT ReserveGroup
>IF !SEEK( nGroupToLock )
> INSERT INTO ReserveGroup VALUES ( nGroupToLock )
>ENDIF
>IF LOCK()  && lock the record
> lLocked = .T.
>ELSE
> lLocked = .F.
> WAIT WINDOW RecBusyMsg
>ENDIF
>SELECT ( cTheAlias )
>RETURN lLocked
>** End LockGroup