Refresh Problem with 2 dependant Combo Boxs in a data sheet

[chimed]

Hi I'm working on my first Access database.

I've had a lot of trouble getting one combo box to limit the list of another combo box, but finally got that 'working'. The problem is that these combo boxes are in a datasheet with lots of rows and whenever I change my catagory field (In the Catagory Combo Box) the previous product selections (In the Products Combo Box) disapear.

This is my present AfterUpdate in Catagories Combo Box.

Private Sub Combo45_AfterUpdate()
Me.[Product ID].Requery
End Sub

I'm sure there must be some simple procedure I've missed and would be most grateful to be put back on track.

Thanks
Chimed