iPhone Getting 1600 error Iphpne 3g

[CROSP]

Hi everyone ,
I have Iphone , I am trying to update custom firmware but always get 1600 error, I have tried everything , but nothing helps.
When I try to update offical 4.2.1 firmware in iTunes - error 1015. But it is possible to update offical firmware through the redsnow (Select IPSW). Everything is ok than. Also there is possible to update 3.1.3 custom firmwares such as whitedoor ,blakdoor and so on.
But when I try to update 4.2.1 custom firmware I always get 1600 error.
Of course device is pwned dfu, I have comment row in host file ,but nothing helps.
I want to update custom 4.2.1 firmware .
Hope, you can help me to solve this problem.
Thx in advance.

P.S phone is locked .

 

[CROSP]

Problem is solved !!!
I tried to pwned my device without "Select IPSW" , selecting original 4.2.1 firmware in redsn0w .
If you have same problem , try these steps.
It doesn't matter what baseband do you have , but note if you have 06.15 baseband firmware you will get 1015 error in iTunes while updating on offical firmware.
If you want to install offical firmware , firstly downgrade modem firmware thru redsn0w.
Also you must have redsn0w 0.9.12 and lower , if you try to pwned your device in redsn0w 0.9.15b3 you will get "USB Communication problem".

- If you have iOs3 firmware you should
update it to 4.2.1 in iTunes. Getting
error 1015 is ok , it means that your
modem is 06.15.
- After updating on offical firmware
turn off your device and open redsn0w
than click "Extras" -> "Select IPSW"
select official 4.2.1 firmware ,
click ok and return to return to
"Extras" and choose "Pwned DFU". And
follow instructions.
- Congratulations ! Now you can install
any custom firmware !!