Why can't I make Combo Boxes on the form frmRespiratorScreen that work?

PROBLEM
On the screen frmRespiratorScreen when I place a Combo Box on the screen it does not work.

TO RECREATE THE PROBLEM
1. Add a lookup field that pulls from any table in the tblSilica1 table.
2. Add the newly created field to the query QrylSilica1
3. Open the form frmRespiratorScreen
4. Put the form frmRespiratorScreen in design mode
5. Select Add Existing Fields from the Toolbar
6. Put the form frmRespiratorScreen in nForm View
7. Try using the Combo box
Silica_App---ExpertsExchange.accdb