When I create a unique identifier (UID) before creating the UID attribute, then create the UID attribute, re-open the UID and move the new UID attribute into the UID, click OK or APPLY in UK constraint dialog and OK or APPLY in the entity dialog, I get the error message "Incomplete Unique Identifier definition". I go back into the UID and the UID attribute has moved back out. Solution is to delete the UK Constraint, click APPLY then create the UID attribute.