Hi,
Check the event logs on the server and workstations for any errors, they usually give pointers to where the problem lies.
Also how many Workstation are in the Network.

>>> Let me know whether it solves the problem.
>
>Unfortunately it has not!
>
>Think it has something to do with workstation losing connection to server.
>
>Strange thing is now we have character field first we can see "SMB." in field then control characters. It's happened twice in last week and both times "SMB." appears, Character field has not protected any fields, still corrupts to same point.
>
>
>Gary.