#NAME? error in sub-form combo

I have an unbound flex-grid form with a sub-form in it that is displayed in
datasheet view. There are several fields in the sub-form, two of which are
combo boxes that refer to two different lookup tables. The source for the
sub-form is a query. The first combo field works great. The second one
gives me the #NAME? error and says it can't find it. But if I go to the
query - it's there, and the combo works in the query. If I backtrack to the
table, it's there and works as well. It's just that particular field in the
sub-form. I've deleted the field and put it back in - same result. I'm
working in Access 2003. Ideas?