Forms :: Form For Adding When Not On List

I have a table Department

ID
DEPARTMENT
DEPARTMENT_EXPLINATION

I have a table Employee_Listing..This table includes:

Employee_ID (Primary Key)
LAST_NAME
FIRST_NAME
INITIALS

I have a table DISCREPANCY_LIST..This table includes:

DATE (Auto completes to current date)
EMPLOYEE_ID (Primary Key) (Brought over from Employee_Listing via form when initials are entered on form)
LAST_NAME (Brought over from Employee_Listing via form when initials are entered on form)
FIRST_NAME (Brought over from Employee_Listing via form when initials are entered on form)
INITIALS
DEPARTMENT
NUMBER_OF_UNITS
NUMBER_OF_DESCREPANCIES
NUMBER_OF_OK_UNITS

I have a form - DISCREPANCY_LIST..This form enters information into the DISCREPANCY_LIST table.The initials combo box is set: Limit to List Yes and Allow Value List Edits No If the user enters initials that are not stored in the Employee_Listing table they receive an error. Instead of an error I would like for them to receive a message asking if they would like to add these initials to the Employee_Listing table.If the user clicks Yes, then it will bring up the Employee_Listing form.If the user clicks No, then they are told to enter valid initials.