>that is a suprise. please let my know what your findings are, once you figered out how they where created.

The findings are still not perfect. I added a SYS(1104) command just before the unlock in order to assure that the data is written to disk. But, I suspect this command doesn't work exactly as it is suppose to be as I still have duplicates. Those duplicates are clicks issued by the same user at the same time. So, the locking mechanism seems to be ok but once the other app gets the lock, the LOCATE doesn't see the new added record, thus it add a new one with the same values.