Not knowing the rest of the design, I figure it's probably something simple...
Did you check the box allowing records to be created via the relationship?
File>Manage Dbase>Relationships tab
double click on the relationship and look at the check boxes along the bottom...if the box isn't checked, you cant create a record except in the table on which the layout is based. That sounds like what you're describing.
That was the problem... Solved. Thanks Ninja!