Those who upgraded their iPad to iOS 4.3 Beta are having a lot of problems in downgrading the iOS version to 4.2.1. Everytime they try, their iPad goes into recovery mode and ends up with 1015 error. Those who have a developer account can easily go back to 4.2.1, but not the normal users that obtained it from torrents and other places. We, at iPadhype, found the solution and it is simple!
You have to options now.
1. Wait until Apple releases iOS 4.3 to the public
2. Follow this method.
First download the iOS 4.2.1 and restore it. It will enter into recovery mode. Immediately run Greenpois0n (I tried RC5_2). Then activate via iTunes. Now, go outside and get some fresh air.