I went to unroot my phone today, everything seemed to go fine, but then while it was updating from the PG0IMG.zip, I received this message:
"Main Version is older!
Update Fail!
Press <POWER> to reboot."

When I press power to reboot, it immediately enters HBOOT. I tried deleting the PG0IMG.zip file. Still went immediately into HBOOT. I tried using the newest RUU for the latest ICS update on Thunderbolt, and it returned the same message. Help??