Error 1601 in iTunes when trying to restore a custom firmware
This is what your looking for:


http://www.iphone4jailbreak.org/itunes-restore-error-1601-1604-1600-fix.html


There's also some other possible solutions for the error 1601:


http://www.simonblog.com/2008/09/25/winpwn-error-6-1600-1601-1604/
http://modmyi.com/forums/pwnage/281841-error-1601-help-please.html