PROBLEM: HTTP Response Code 417: Expectation failed.
Example: HTTP Response Code 417: Expectation failed.
SOLUTION:
Some proxy servers interfere with the HTTP packets sent between client and servers on a network. The .Net HTTP layer adds an 'Expect: 100-Continue' header that some servers choke on and return a 417 error. The solution is to configure the \Windows\Microsoft.NET\Framework\v2.0.50727\CONFIG\machine.config file and merge the following configuration into the XML.
<system.net>
<settings>
<servicePointManager expect100Continue="false"/>
</settings>
</system.net>