Will not restore or upgrade
iPad 2, iOS 5.1.1, jailbroke. Win7x64, iTunes 126.96.36.199.
After getting an iPhone 5 with iOS 6.1 on it, not jailbroke, I've decided that I really do not need jailbreak on my iPad anymore and I'd prefer to upgrade it to iOS6 so I can install some apps that require the current OS. Prevailing wisdom, as I understand it, says that to un-jailbreak all you need to do is plug it into iTunes via USB and tell it to "restore".
It does not restore.
I get an error that says "Cannot restore this iPad due to an unknown error".
I've tried doing a straight upgrade, a straight restore, and via DFU (hold power and home while plugged in until the iPad says to connect to iTunes). In every attempt, iTunes says "unknown error" and does not proceed. I also tried uninstalling all of the Cydia apps I've previously installed.
I did do a restore and re-jailbreak at some point last year, and the only significant change I can think of since then is some "critical updates" for Cydia the other day, that came out after Evasi0n was released.
The good news is, I do not (yet) appear to have lost anything off the iPad. What is my next step? Using the on-board "erase all content and settings" and try again? Or something else? I certainly cannot take it to Apple as it currently is due to the current jailbreak.