Can not Access a URL using Webrequest

I am trying to get access a URL using .Net but when I run my Program I get the Error The remote server returned an error: (403) Forbidden. Now, the issue is if I click the link http://thisIsMyUR, and enter the user name and password as in the below code. It totally works. I am not able to understand why this exception is coming? Please refer the code below.

Side Note: I am using this sample function below to fire Build of my project in Jenkins Server.

string url = "http://thisIsMyURL";
WebRequest webRequest = WebRequest.Create(url);
webRequest.Credentials = new NetworkCredential("admin", "pass");
WebResponse response = webRequest.GetResponse();
StreamReader reader = new StreamReader(response.GetResponseStream());
string responseText = reader.ReadToEnd();