users who are experiencing 2003 error when upgrading firmware to IOS 4.2.1 through Itunes 10.2...the reason is the computer itself. I personally experienced this problem and got really frustrated and scared at the same time thinking that I had ruined my nephew's Iphone. I used 2 computers with Windows XP. These computers are not up to date. So I decided to use the newer laptop which was purchased this past Christmas with Windows 7 and problem was solved! I hope this info will help some people who are getting the "2003" error when doing firmware upgrade.