Using a VPN product called iLink by Cognitas, being on a VPN produces URLs in the following format:

https://proxy.domain.com/the-url-you-actually-want

For example https://webtopxeu7.domain.com/http://internal.ourdomain.com/Site/default.aspx

The issue comes when trying to use the $.ajax function from URLs like this. Attempting to reach "/Site/Segment.aspx", the error returned is "Invalid argument" taking place on line 5113 of jquery-1.4.2.js.

Stepping through with the IE8 debugger, the psSRAPRewriter populates the lURL property on line 9550 as "http://internal.ourdomain.com/Site/GET" and therefore gives an invalid response. The three (magically) inserted values are:

var requestNetworkURI = 'http://internal.ourdomain.com';

var requestBaseURI = 'http://internal.ourdomain.com/Site/';

var gatewayURI = 'https://webtopxeu7.domain.com';