I used to see this error very often running on a Novell network - admittedly a long time ago.
My tables were old FoxPro 1.02 tables, updated by a compiled FoxPro 1 application. I was using FPW to access them and repeatedly had this error when using LOCATE.
I discovered if I waited 5 seconds after a user had added a new patient record (just lisening to the keystrokes and the dictation machine!) then it would work just fine. So it seemed to be a network update speed problem, updating the indexes and table.
Moving to all FPW and to a structural .CDX fixed the problem.

I haven't seen this error since moving to all Windows platforms, and of course to VFP.