Why are you trying to re-lock? Taking a phone back in for repair? There is much info out there about this, but I had to take a phone back in and swap it for a new one a while back. What i did rather than using a re-locking program was just simply re-flash a stock rom. It worked perfectly, re-locked the phone and had no troubles turning it back it for my new one.
Here is a link WDM posted for stock ROMs
http://forum.ppcgeeks.com/showthread.php?t=73894