Order Form - Issue with Fields set up as combos

Hi

Hope someone can help me. I'm trying to set up an order from in Access 2003
and being very rusty have been using a Microsoft template.

I am setting up an employee ID box that I want to show the employee name:

I have a qry (Expr1: [LastName] & "," & [FirstName]) that has added the first
and last name together and it appears on the form in the correct format but I
immediately get an error message : The value you added isn't valid for this
field. I have set up the qry against the * not employee ID.

The PK is Employee ID.

I have the same issue with Customer ID.

Am sure this is something simple that I have overlooked.

Thanks
Diane