A family of Microsoft relational database management systems designed for ease of use.
I agree that there's some stray code causing this. Try typing Ctrl-G to open the VBA editor and select Debug... Compile to compile the database's VBA project. Correct any code errors.
You may also want to post the form's and subform's Recordsources (post the SQL) and the Master and Child Link Fields - one of them might be flawed.