When a WINS server is removed from the replication network, its' entry is not removed from the WINS database of the other WINS servers. These entries are replicated indefinetly.
To remove these PersonaNonGrata, edit:
Add Value name PersonaNonGrata as a type REG_MULTI_SZ. Set it to the IP address of the non-existent WINS server. If there are more than 1, each IP address is entered on a separate line.
Stop and restart your WINS server. You can now use WINS Manager to delete it is an owner.