Is this a consistent problem for all the apps you have, for example if you just get a sample app and try to build it you get the same issue? If so there's a good chance it could be your firewall or proxy. If you can try removing the proxy and connecting on a different network (e.g. home network or wifi hotspot) to see if you can connect that way.
I imported a template, tried to build it and I got the same problem. The last chance I have is to change of network but I am not very sure if it'll work or not.
Thanks for your feedback!