This device isn't eligible for the requested build

I have an iPad 1st gen with with iOS 4.3.5 is the current software version. I am trying to upgrade to "iOS 5 beta 6", but I am getting this error message

This device isn't eligible for the requested build

note: - my iPad device is a registered development device. - I tried removing the gs.apple.com entry in localhost file, reboot itune/my mac etc but it didn't work. - I have iTunes 10.5 beta 6 installed on my MacBook. - I am running Lion - OS is u开发者_StackOverflowp to date.

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I guess the questions is now, any idea how to locate iOS 5 [beta 1 to 5] files on the developer website?

Are you asking where the betas are? If you log into the iOS Dev Center, there is a tab up top called "iOS SDK Beta" and it looks like there is a beta for iPad 1 (but not iPhone 3G).