>Look at the tables that the cursor gets its data from for an index key expression problem.

Is this a clue?

The problem only occurs ONCE per session.

In other words once I've ignored all the error messages and it does what I wanted it do in the first place, I can then repeat it in the same form/table combination - or any other form/table combination with no further protest. But if I exit the app then I'll the problem the first time I try it on re-entry.

Does this tell us anything? If so what?