You need to delete DC and TopLevelDCs both, and then you can create DC again.
Logon to DTR:
Find the path /ws/<TRACK ID>/<namespace>_TRACKID/dev/inactive/SCs, find <dc name>.dcref,and delte.
Find the path /ws/<TRACK ID>/<namespace>_TRACKID/dev/inactive/DCs, and delete the DC directory.
Wayne