When you run TU it sets the host for the apple server to Saurik's SHSH blob server, unless you specifically uncheck this in the options.
Not sure on your competence with computers so here goes.
First you need to edit your host file:
Saurik's Instructions [Caching Apple's Signature Server - Jay Freeman (saurik)
You need to put a'#' in front of this bit '126.96.36.199 gs.apple.com' this makes Apple the default server again in your host file. If you run TU again it will default back to Saurik's Server afterwards.
The reason for doing this is that since Apple changed some parts of iTunes in 10.2.1 etc that it keeps failing to do a proper DFU restore.
Now put your iPad into DFU mode and do a restore.