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Did you post anything on the apple developer forum regarding your issue?
 
Things to note,

Make sure SDK is installed.
When you go to do the update, do it through XCode and not iTunes.
Then go back into iTunes for the restore.
 
This build requires you to be authorized in the developer program to continue to use beta2. This means if your device ID is not added to the PAID developer program you will NOT be able to use 4.0 beta 2.

It's extremely important to note that this build has extra security measures. If you erase your phone to do a clean install of beta 2, and are NOT an official iPhone developer with a paid account, and don't have your iPhone's ID added in the developer portal…YOUR PHONE WILL BECOME 100% a paperweight.

Apple added in with AT&T that your phone will NOT be allowed to activate. This means you're phone will no longer work even if your chose to restore it (YOU Can't if you installed 4.0 beta 1.

FYI beta 1 expires in a few days. So for those of you who illegally installed it on your iPhone, it will become a paperweight in a few days unless you join the $99 iphone program.

You've been warned. I'm an official dev, so I can add my device IDs to the program, but before I added my second 3GS's device ID to developer portal it would not even allow me to activate the phone. as you can see from the screenshot this is what happens when you try to install 4.0beta2 without having a real iphone developer account.

Your choices right now are spend $99 and hope you get accepted to the iPhone developer program or enjoy a bricked phone in a few days when beta3 is installl,
 
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