Is it an iTunes error? If so, trying using another computer to perform the restore. I was having a problem updating and restoring, and I tried it with a different computer using iTunes. It worked perfectly, and I synced it back to the original computer.
What error message are you getting? My brother's iPod wasn't restoring on the home office PC when he had forgotten his password. Have you got access to another computer with iTunes, if so try that as that worked for me when I was fixing my brothers iPod.
They have stopped signing all IOS 5.1.1 and lower! That means you cant downgrade or restore to a lower firmware or to the firmware you were on, You HAVE to update... Sorry