Try iReb r7 on iOS 6.1.3 to Fix iTunes Restore Errors [1015 / 1600]
Download ireb 7 version now and bypass iTunes errors when downgrading and restoring. iREB utility designed specifically for Windows users, which at the time of recovery on custom firmware (created with Pwnagetool or Sn0wbreeze) appear iTunes error 1600 or 0ther like 1015, 1604, etc.