Unable to assign a DFL Store to the MXC EOM Pilot Zone

Scenario - I want to allow a DFL Store Access to EOM so that the requirement for Transfer Expenses FROM a DFL location to a Standard location can be met. 

Steps:

1.Login to MMS 

2. Navigate to the Zone Manager 

3. Attempt to assign stores to the MXC EOM Pilot zone

Defect: 

System displays a message: 

NOTE: I can remove the current stores from the ZONE but then I am stuck. I can no longer add them back.