Initial patching does stop early. That is normal. After you try to run the game the first time it will continue patching and then fail on 5.0.6d (that is what you want it to do) - but 5.0.6c will be intact. Don't delete the 5.0.6d read-only RTP! If you do, the game will be able to patch beyond where you want it to. Just leave it sitting in the UO patch folder.
Then try logging in via ConnectUO. You will want to use ConnectUO to log in, as this allows you to get the shard patch (which is different than the UO patch for the game which you did above).
Good Luck.
GhostRiderGrey