We have a transparent proxy at work, and it was causing troubles in Visual Studio 2012 when going to the Extensions and Updates. Contrary to your expectations, “The remote server returned an unexpected response: (417) Expectation failed” message was appearing. The fix is pretty easy, and involves editing devenv.exe.config file in the Visual Studio 2012 folder (normally C:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\IDE\). Somewhere towards the end of that file there is a
<system.net>
<settings>
<ipv6 enabled="true"/>
</settings>
</system.net>
fragment, which has to be fixed to read
<system.net>
<settings>
<ipv6 enabled="true"/>
<servicePointManager expect100Continue="false"/>
</settings>
</system.net>
That’s it.
Roman Hnatiuk 