i am trying to jb a 3gs running 3.1.2/05.11.07 (simlocked, never jailbroken before) using custom firmware. i've downloaded iPhone2,1_3.1.2_7D11_Custom_Restore.ipsw, but whenever i try to restore it, i get 16xx errors from itunes (mostly 1604). i get these errors in dfu or recovery mode, too. ireb does not work. what am i doing wrong? is blackra1n the only option for 3.1.2?