You may have a query that is not-updatable. That is pretty normal for
complex queries and certain classes of queries such as GroupBy and
Union queries that are never updatable.
Sometimes DISTINCTROW will make a query updatable.
I bet Tom is correct about the record set not being updateable. If the form
uses more than one table, you probably need a form based on the parent table
and a subform based on the child table. Also make sure that they are linked
using referientialintegrity in the Relationships window.