Error 1600 on Downgrading iPod Touch iOS 5.1.1 to 5.0.1

Hello experts,
HELP!! I've been trying to downgrade my iPod touch 4g IOS 5.1.1 to IOS 5.0.1 and this happens every time.
I restore it (shift click restore) and after waiting, it says "THE IPOD COULD NOT BE RESTORED. AN UNKNOWN ERROR OCCURRED (1600).
I Have been researching how to fix this problem, but it just keeps doing it all over and over and over again.
So basically, I just had enough dealing with it. I don't know what else to do.
So, PLEASE HELP ME!!!
Thanks so much.
