Access 97 - Runtime error 2448

I have a form which contains two sub forms (sub1 and Sub2), each form has
only one table as the record source. The forms are linked to the main form
by the date and the user. The main form keeps track of or summarizes the
info entered in the sub forms. Sub2 is a datasheet that allows the users to
enter multuple records. The users are getting " run time error 2448 - you
can't assign a value to this object " when entering some records. I have
researched the error and found that is has to do with the buildCriteria,
however, I am not using the buildCriteria.

Any suggestions.

Thanks