New record results in blank foreign key in subform

Hello,

I have a form with a subform. The mainform has a primary key ([ID]) and the subform has a foreign key ([MasterID]). When new records are added in the mainform, I get an error message that says, "ODBC -- Call Failed." The error message goes on to say that it cannot insert a null value into the column [MasterID], the foreign key in my subform.

[ID] and [MasterID] are in a one-to-one relationship. The data in the main form represents information at an initial state and the data in the subform represents an end state.

The error message seems to happen before the form's Before Insert event, so I am really at a loss as to how to fix this. I am new to SQL server. The backend files are on SQL server and the front end is running on Access in an MDB file.

Thanks,
JoshSorry, I figured out what was going on - my relationship was not set up correctly. I had test data in my child table with no parent. This caused the relationship to save incorrectly.