Unknown Error 3002 when upgrading iPad to iOS5

I have been trying to upgrade my iPad to iOS 5, and I have been trying for almost an hour but I always failed due to the unknown error 3002. The iPad is in iOS 4.2. I was installing the upgrade through iTunes 10.5.3.
How can I fix it?

iTunes
The iPad “iPad” could not be updated. An unknown error occurred (3002).
