Hey all, I've been trying and reading all day and all yesterday for a solution but i haven' been able, this is my situation:

I had the 3GS on 4.1 in locked state, restored to 4.2.1 and then I used RedSn0w 0.9.6b and did the normal process with the iPad FW and I had no problem there, redsn0w then got stuck in Installing Activation Bundles, and I had to hard reset, after I did that I got access into the phone but the springboard disappeared except for cydia!
I restored again waiting for the obvious firmware error since the BB is currently on 06.15.00 and after this I got the connect to itunes screen.

I tried to get it off recovery mode with:

TinyUmbrella
Ireb
Restoring again

with Redsn0w rebooting on tethered mode, adding cydia again then DFU mode, downgraded to 4.0.1 (itunes doesn't let me use any other firmware no 4.1, 4.0) and the same revoery mode screen pops up, then I wen't again to 4.2.1 and the same screen appears (recovery mode) i've tried everything and nothing, same screen....

Please help!

Obviously you didn't read all of Dev-Team Blog - Ultra-recycle properly before attempting this risky update.

Read this Howto: restore iPhone 3G, 3GS running 6.15.00 BB - Hackint0sh, and post in that thread if you still have problems.

Thread closed, duplicate/known problem