[visual-studio] Visual Studio Error: (407: Proxy Authentication Required)

I was getting an "authenticationrequired" (407) error when clicking the [Sync] button (using the MS Git Provider), and this worked for me (VS 2013):

..\Program Files\Microsoft Visual Studio 12.0\Common7\IDE\devenv.exe.config

  <system.net>
    <defaultProxy useDefaultCredentials="true" enabled="true">
      <proxy proxyaddress="http://username:password@proxyip:port" />
    </defaultProxy>
    <settings>
      <ipv6 enabled="false"/>
      <servicePointManager expect100Continue="false"/>
    </settings>
  </system.net>

I think the magic for me was setting 'ipv6' to 'false' - not sure why (perhaps only IPv4 is supported in my case). I tried other ways as shown above, but I move the "settings" section AFTER "defaultProxy", and changed "ipv6", and it worked perfectly with my login added (every other way I tried in all other answers posted just failed for me).

Edit: Just found another work around (without changing the config file). For some reason, if I disable the windows proxy (it's a URL to a PAC file in my case), try again (it will fail), and re-enable the proxy, it works. Seems to cache something internally that gets reset when I do this (at least in my case).