SYMPTOM:
In the Strategy Developer 9.x, when deleting an address from a contact in the User Editor > Deliveries > Addresses, the following message is displayed:

ACTION:
Check if there are multiple addresses which have the same 'Name' and/or 'Physical Address', refer TN: 36878 and make sure each address has a unique name and physical address.
If the address has a unique "Name" and "Physical Address" and still getting the error message, use the following workaround to delete the address.
WORKAROUND:
Use Strategy Command Manager and run the following script to delete the address.
REMOVE ADDRESS "addressname" FROM USER "username";
REMOVE ADDRESS "Outlook" FROM USER "Test";

Note: the address that is trying to delete may not duplicated, but in the Addresses list, there is other addresses have either same address "Name" or same "physical address". Check all the addresses from the list and correct duplication.