I probably know the answer to this: Can't Be Done.

BUT...

I have a form with DtTrngStarts and would like a pop-up if the date entered is before DtRegistration that exists in main table of a one-to-many relationship.

I can do pop-ups for validating based on fields in the same table, but can't get syntax right for this. AND I have no real pupose to do sub-form.


Any ideas?
Thanks.

Try doing a Dlookup to get the dtRegistration from the main table. Then compare that to the dtTrainingStarts that your user just keyed in. I'd probably do this in VBA, in the After Update event...not sure, but that sounds right. You could do then put out a msgbox.