Wordpress API not found error

Question

I'm trying to call an API on our web server that allows us to create a user account in a Wordpress site.

If I enter the URL into a browser it works fine. If I try to call it via code it comes up with the following error : -

The remote server returned an error: (404) Not Found.

This is the code that I'm using

string URL = "http://api.mywebsite.com/pol-wp/api/user/register/?username=john&[email protected]&nonce=7706960c14&display_name=John&notify=both&user_pass=xxx&insecure=cool";

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(URL);
request.Method = "GET";
request.ContentLength = 0;
HttpWebResponse response = (HttpWebResponse)request.GetResponse();

Update: Pasting the URL in Chrome works fine , but pasting it into IE produces the 'Not Found' error message