sorry, probably a dumb question

[Squirrel240sx]

i tried searching all over but maybe i'm searching for the wrong thing
my iphone 3g was downgraded to 3.1.3 from 4.0 (too laggy) and now won't allow me to install ANY other firmware. i've tried 4.0.2, 4.0.1, 3.1.2, and the phone just reboots when i try upgrading in itunes. after the process it's still on 3.1.3 and itunes gives me error 21 could not complete upgrade or whatever. thoughts?

it also gave me problems when jailbreaking 3.1.3. redsn0w wouldn't work, it would just reboot to a black "off" screen when i tried putting it in dfu mode during the jb process and be stuck there until i did a restore in itunes. i had to use a friend's sim card to get past the activation screen and jb over at jailbreakme.com. i'm just a little confuzzeled. coming from a touch pro 2 which, imo, was extremely easy to unlock & upgrade. i don't get all this iCrap.

[schettj]

Why did you fsck with it if you don't understand what you're doing?

My guess is you borked the downgrade. Are you trying to upgrade from Mac or PC?

Try putting it in DFU mode, and restoring the desired firmware, from a NEW user account on your Mac/PC.

DFU mode: http://iphoneindia.gyanin.com/2009/1...toring-iphone/

The "fix" for error 21
http://forums.macrumors.com/showthread.php?t=975858
http://discussions.apple.com/thread....ageID=11723151

Here let me google that for you: http://www.google.com/search?q=iphon...pdate+error+21

[Squirrel240sx]

I'm on a pc. Thanks for the info. I'm pretty sure i did the downgrade correctly. I followed the instructions for that exact and used recboot to get past the 1015 error code. That all worked fine other than redsn0w not working to jailbreak. But jailbreakme.com worked great so not a big deal, I guess.
I searched all over google for error 21 and all I came up with was the stupid apple help page suggesting antivirus which is obviously not the problem and threads where ppl asked the same question but got no replies. Guess I didn't look deep enough. I usually give up after I go through more than 5 or 6 pages of google and don't find what I'm looking for.
I'm not new to messing with smartphones, just new to iPhones.

[matticrew]

i have had error 21 be a battery before , many times