Are you using the the rom from the link I gave you? cuz thats the one that supports the xda unlock, I remember when I had the tmobile rom on the phone and tried to unlock the phone, I got the same error as you did..but when I put the new rom (step by step) from the link, I just used xdaunlock and boom, just like that, it was unlocked...

I guess you're not getting the same luck as I did, good luck...