I updated my 3G with the latest software and now I get the dreaded Error 21....I've tried the solution that worked last time with no joy. Put it into DFU and tried recover but just keep getting the error.
I just want to restore it to get rid of it. My contract is up and if a company can give updates that mess your phone to this extent then I don't want to try another iPhone.
Has anyone any ideas on how to fix Error 21......I'll try a few more times, but am going to the apple store on Monday and tell them to fix it.

I would go to the apple store on monday and tell them to fix it.

There seems to be a few people who have the same issue here and about halfway donwn someone seems to have a workaround http://discussions.apple.com/thread....72677&tstart=0

TBH considering the number of problems iPhone 3G owners have had with iOS 4 they should have just made it for the 3GS and above. Even once you update it it's really sluggish anyway on the 3G. And even some people with the 3GS had issues!

I know this doesn't help you OP but all I can think of is DFU mode. But you've tried that

Interesting it seems to indicate it's an iTunes issue. If creating a new user and doing the software update from a fresh profile works...

I had already tried that work around but had another go. In the end I created six different user accounts, but, it's been successful.
Saves a 20 mile trip to the Apple store.....Got it up and running. will be able to sell it now to fund Galaxy S..........Maybe!!??.....

Hm, what's going on. Apple used to be quality, overpriced but quality. Now it's one problem after another. Somebody should give Jobs a book about quality management as a gift.