DLookup Issues in Access

I have a form that I need to lookup the value of a field based on two other fields on the form. I have a table that contains all of these values. I have a DLookup function that I thought would generate the output I wanted but when I put it as the control source for the field I need to be looked up nothing appears in the text box or #Error appears. Here is what my DLookup looks like:
=DLookup("BranchNo","tblAllADPCoCodes","ADPCompany='ADPCompany'"&"AND LocationNumber='LocationNo'")