I was having the same problem on several of my networks in Kuwait and Iraq. I beat my head against the wall on this for a week. One of my guys finally fixed the problem for us with one simple setting change.
1. Make sure IE is not running
2. Go to the Internet Options Control Panel
3. Click Advanced
4. Uncheck use HTTP 1.1 & Use HTTP 1.1 through proxy connections
5. Click Apply and OK
That's it. It has worked perfect for me since!
- - Ohhzone...