I am trying to query some URL using WebClient.
I have a collection which I loop through to get the QueryString value, and build final URL,
Some web servers can block requests based on the user agent string they provide. In your case, you send an empty string as a user agent. Try to add the user agent of a browser, any browser would be fine.
For example:
client.Headers.Add("user-agent", " Mozilla/5.0 (Windows NT 6.1; WOW64; rv:25.0) Gecko/20100101 Firefox/25.0");
For a list of user agents, you can click here.