IPSW IS NOT SUPPORTED BY THIS VERSION

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I HAVE IPHONE 3GS UPGREDED 6.1.6. I WANT TO JELLY BRAKE IT ,MODEL NO-A1303,I DOWNOLAD Redsn0w 0.9.15b3
AND IPSW 2,1_6.1.6_10B500_RESTORE AND FOLLOW 1 TO 4 STEP BUT AFTER SELECTING IPSW THRE IS ERROR SEEN LIKE THAT IPSW IS NOT SUPPORTED BY THIS VERSION OF REDSNOW ...PLS HELP