The request failed with HTTP status 417: Expectation Failed - Using Web Services
This suggests that the problem is a proxy server that does not support a 100-continue response from the server, and shows code for resolving it. This would explain why it works on another network.
Since you are unlikely to convince your ISP to change their practice (no harm in a request though), you should turn off the behavior of sending a 100-Continue as the link suggests by either:
Putting this code before an web request:
System.Net.ServicePointManager.Expect100Continue = false;Or, adding the following lines to the applications configuration file as a child of the <configuration> tag:
<system.net> <settings> <servicePointManager expect100Continue="false" /> </settings></system.net>
Add below line of code in your config file.
<system.net> <defaultProxy useDefaultCredentials="true" > </defaultProxy></system.net>