Thanks so much for your response Tony. May I say that I am very impressed with the grid control and very much appreciate your sharing this with the community.

I'm sorry for the confusing details.

As you've already diagnosed, it has nothing to do with the my orignal theory of the number of items or the contents of the item data. However, I have NOT tried looking to see if my ID fields are unique in both cases. That makes perfect sense and I should have checked that first.

I am multi-tasking between three projects at the moment so I will try this and report back as soon as I can.

Thanks again for your help.

peter