Do all workstations/users have necessary privileges on Win2k Server shared folder where the DBC and tables are? Connect as Admin from all workstations and see if you get same bad results.

>PK are taken form a table where lock record,take number,increment number,update table,unlock record
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>In server there are 3 net cards with 1x24TX100 switch eachother problems are on every net branch => can't be all 3 switches bad