I'm trying to restore iOS 5.1.1 on iPhone 4 GSM that currently has iOS 4.3.3 and is jailbroken.
I'm using "redsn0w" to get into pwned DFU mode and then trying to restore from iTunes using custom IPSW file stitched with the 5.1.1 shsh blobs (I have my shsh blobs saved locally).
It works until iTunes reaches the point
Preparing iPhone for restore.
At this point my iPhone automatically exits the DFU mode and enters into restore mode, but iTunes stops restoring with the error
iPhone could not be restored. An unknown error occurred (21).
I have checked the hosts file and have commented the line that redirects to the cydia server. (I have also checked it by uncommenting that line but it still didn't work)
Any idea what could be going wrong or is there anything I'm missing?