Now I know the values in the field in question are unique – I have only 3 records.

But when I delete all the records from the table, I still get the above message.

<SL> Are there other active connections?  Have they committed all transactions?

<SL> FB Indexes contain information for **all active transactions**, so if there are active transactions which can still see the old data … adding the new constraint would fail.

Thanks Sean,

I didn’t think so but it’s possible – I’ll defer on this one.
Alan