Is there a way to go from 4.2.1 to 4.3?
What error did you get, exactly?
It does not matter what blobs you have. For the iPad1, the most current software is iOS 5.1.1. If you follow the tutorial - backing up both App Store and Cydia apps, then putting your iPad in DFU mode to install iOS 5.1.1 (stock) - then you'll be able to re-jail break the iPad1 on iOS 5.1.1.
You cannot go from jail broken on one iOS to jail broken on another directly; you have to move from jail break iOS, to stock iOS, then jail break the new iOS.