RICH, the reason I don't use field required is because the command button launches a subform that is linked to the table in a 1 to 1 relationship, only when certain criteria are met.
I think I've solved the issue, in table design when you select number field type and integer, Access automatically puts a 0 in the default field value (how kind of it). When I selected any of the combos, the other fields on the record became 0, so the fields being tested were neither empty or null. Very annoying and very simple problem....you live and learn!