Go to your form properties (Data Tab) and find the property "Recordset Type".
It probably list the type as Dynaset. If you change it to Dynaset
(Inconsistent Updates) this should work.
However, you need to understand what happens when you change to Dynaset
(Inconsistent Updates). You can set yourself up for problems with orphaned
records in the many side of a relationship by setting this property this way.