I work behind a firewall on windows and I have the Same problem. But I managed to fix it:
cmd
then hit Enter (displays the command prompt)netstat
In the results returned, find your Proxy address :
TCP YOURMACHINENAME:PORT DISTANTMACHINE1:PORT
TCP YOURMACHINENAME:PORT DISTANTMACHINE2:PORT
TCP YOURMACHINENAME:PORT DISTANTMACHINE3:PORT
Your proxy address is one of the DISTANTMACHINEx