IPHONE 3GS This device isn't eligible for requested build

Question

Well with all the crazy troubles with iOS 5 I thought I'd share some help with the community since I finally got mine to work.
I have a iPhone 3Gs and 4.3.5 never jailbroke it but I did install Tinyumbrella as a precaution just incase I ever needed to downgrade for whatever reason.
I attempted to update but since I was still texting I downloaded the update to my computer first. When I backuped, synced and everything else just to make sure my data is safe. I tried to update.
This is where my troubles started. I couldn't get my device to update. I had it downloaded so what was the problem. I searched high and low for the answer and nothing was coming up....well nothing recent that would have to deal with iOS 5 and my 3Gs. So I did a little digging.
People kept talking about editting hosts files and changing ip addresses for whatever reason and being a recent convert to Apple I was still not getting it fully.
So here is it in a nutshell.
1. Open the Terminal utility. For newer users it is located in the Utilities folder.
2. Type in (without the quotes) "sudo pico /private/etc/hosts". You may have to enter a password for admin rights.
3. A screen will pop up and hopefully you will see a bunch of words looking like this....
# 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
##My Ecenica Hosting Websites
100.100.100.100       example.com
4. If by chance you have edited the hosts file uninvertendly the apple ip address may be here. It may look very similar to this "
     74.208.105.171 gs.apple.com"
5. If there is the apple.com ip there you might need to put a "#" infront of it to null/disable that specific line of code. Don't worry it can be undon.
6. Use the arrow keys to move down and in front of the ip address. Again, put a # infront fo the ip address from apple.
7. Control (not command) + O will allow you to save it (there is a small line just about the commands that you will see "write to.....". Hit enter and close the window.
8. Before heading away from the Terminal window you have to flush the DNS. So type in "dscacheutil -flushcache"....hit enter.
9. Close down and try to instal/update again. As I finished this my iPhone has just update and installed. Good luck to all and I hope you all have quick and easy updates!
CHEERS

Answer 1

Try updating iTunes and disabling your security software/firewall.  From http://support.apple.com/kb/TS3694:
This device is not eligible for the requested build (Also sometimes displayed as an "error 3194")
Update to the latest version of iTunes.
Third-party security software or router security settings can also cause this issue. To resolve this, followTroubleshooting security software issues.
Downgrading to a previous version of iOS is not supported. If you have installed software to performunauthorized modifications to your iOS device, that software may have redirected connections to the update server (gs.apple.com) within the Hosts file. Uninstall the unauthorized modification software from the computer.
Edit out the "gs.apple.com" redirect from your hosts file, and then restart the computer for the host file changes to take affect. For steps to edit the Hosts file and allow iTunes to communicate with the update server, see iTunes: Troubleshooting iTunes Store on your computer, iPhone, iPad, or iPod—follow steps under the heading Blocked by configuration (Mac OS X / Windows) > Rebuild network information > The hosts file may also be blocking the iTunes Store. If you do not uninstall the unauthorized modification software prior to editing the hosts file, that software may automatically modify the hosts file again on restart.
Avoid using an older or modified .ipsw file. Try moving the current .ipsw file (see Advanced Steps > Rename, move, or delete the iOS software file (.ipsw) below for file locations), or try restoring in a new user to ensure that iTunes downloads a new .ipsw.