Beta iOS 6 expired on my iPad 3, latest firmware appears incompatible

Got my iPad 3 locked this afternoon, and tried google search and nothing effective so far.

I know my beta iOS6 has expired, so I downloaded the latest iOS6 firmware from a reliable site. My iTunes keeps remind me that the firmware is not compatible with my iPad, either in "Update" and "Restore".

I believe I got the correct iOS 6 file as the name is "iPad3,2_6.0_10A403_Restore", then what can I do to get my iPad back?

I dont want to wipe out all the data and unfortunately I haven't done any back up recently.....

Guys, what can I do?