I wish there was a thread dedicated to this somewhere....
1. Hard reset your phone. (I do this for fun, don't know if it ever helps but couldn't hurt.)
2. Re-Lock your phone if it has been unlocked to run hacked roms.
3. Update with new rom. Leave it alone while it reboots the phone a few times.
Or just read the first post:
http://forum.ppcgeeks.com/showthread.php?t=16806