I Suspect that you might have proxy info cached in registry, Give this a try or else bypass the proxy if possible :)
he legacy proxy settings can be removed by performing the following steps:
1. Open the registry (Start->Run->type "regedit").
2. Go to HKEY_USERS\.DEFAULT\Software\Microsoft\Windows\CurrentVersion\InternetSettings\connections
3. Delete the registry keys "DefaultConnectionSettings" and "SavedLegacySettings".
4. Reboot the machine.
Note: These registry keys will automatically regenerate after reboot of machine.
Also, this also could be caused due to incorrect proxy server information in the following registry location: HKEY_USERS\.DEFAULT\Software\Microsoft\Windows\CurrentVersion\InternetSettings
Removing the incorrect proxy info from this key and then rebooting allowed the client to communicate normally.
One important thing to keep in mind is that any incorrect proxy information must also be removed from the following two locations as well:
HKEY_USERS\.DEFAULT\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Connections\DefaultConnectionSettings HKEY_USERS\.DEFAULT\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Connections\SavedLegacySettings
If the settings are not removed from these two keys, they will repopulate the Internet Settings key after every reboot.
Remove the incorrect proxy information from all 3 registry locations noted above, then reboot.