iOS 5.1.1 Update HELP!!!

For some reason my iPhone 4S is on a reboot loop. When I got it into Recov Mode i tried to upgrade the software (from iOS 5.0.1 to iOS .51) and it gives me the error every time: The iPhone "xxxxx" could not be restored. The device isn't eligible for the requested build.

yes, my itunes is up to date

yes, my mac is up to date

yes, i have restarted my mac/different usb ports

yes, i have put in DFU AND Recov mode (both give same error)

PLEASE HELP ME!!!!