I can't update or downgrade my iPhone 3GS, Firmware 4.3.5 tethered with redsn0w.

Whenever I try to update it, I get a "device isn't eligible" error. I researched on how to do that, like changing host files, but none of them worked for me. I use OS X Snow Leopard.

##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
127.0.0.1   localhost
255.255.255.255 broadcasthost
::1             localhost 
fe80::1%lo0 localhost
74.208.10.249 gs.apple.com

This is my host file – not sure if it's the orginal one or not.