>>Don't forget old favorites like virus scanning or anything that interferes with what VFP expects to be exclusive access
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>Yes, good idea.
>Invalid seek offset is especially scary since there are no dbf's in the system.
>Everything is done with cursors from SQL tables


I've seen those in the past. Are you working with VFP9SP2? If not, that might be a solution.
Another thing to try is to use SYS(1104) at the point where you are seeing this.

We got and huge and complex application used by many thousands of users and we used to see those problems in the early days, but can't remember any recent ones.