A family of Microsoft relational database management systems designed for ease of use.
You lost me. You seem to be implying that there is more than one part number text box.
If you use a combo box instead of a text box to display the part number for the selected customer selected in combo69, then you open the door for selecting a part number for a different customer. I think you should forget this thought and concentrate on getting the arrangement to work. The key things to check is everything about the combo box, the control source of the text box and the names of the controls and fields.