upgrade to 5.1.1 while preserving baseband

Hey everyone, i have an iphone 4 jailbroken with version 4.1 with modem firmware 02.10.04. i want to upgrade to ios 5.1.1 while keeping the firmware the same so it remains unlocked. i used sn0wbreeze and redsn0w and even iREB, but after getting into pwned DFU mode, and opening itunes and shift+restore and clicking the custom ipsw, itunes tells me an error 1601 or 1602 has occured. can someone help me with this? any help is appreciated. thanks

 

the set hosts to cydia box is already unchecked, and if i were to try and check it, the box is grayed out, i cant do anything to it, any suggestions?

 

actually i got it to work, and the baseband stayed the same, and while trying to jailbreak it, its now stuck at the apple logo, any suggestions?