Forms :: Requerying A Combo Box

I am having trouble requerying a combo box.I have created a Drawing Register database which allows users to create a new job as well as set up a drawing register for that job if the use checks a box in the job set-up form which indicates that particular job will have a register.Using the Job-Set up form I created a query which brings pulls the job number, job name and register check box and filtered it to show only those jobs that the box is checked. To this query I also added the relevant fields from the drawing register table. The Job Set Up table is linked to the Drawing Register table by the Contract No. field. Unfortunately I cannot set this field in the Job Set Up table.

Using this query I created a Drawing Register form with the sub-form Drawing Register Details. I added a combo box which shows the lists of all the drawings and allows me to view a specific drawing when selected. The problem I am getting is that the list is showing ALL drawings for EVERY job with a register and not just those drawings for the job I am currently updating. I tried using the following code with no luck

Private Sub Form_Load()
Forms![DwgRegFRM].Form![Combo15].Requery
End Sub

Private Sub Combo15_GotFocus()
[Combo15].Requery
End Sub

I want that when I choose to open the register for a particular job the combo box only lists the drawings for that particular job.