I was searching internet to find how to use HtmlWeb.Load() method under internet service where proxy server and authentication is required. But didn't find the required information. Later on i've figured out the code and now my application is working
find under secured corporate internet where proxy and authentication is must. Below is the code for those who might face the similar situation.
HtmlWeb web = new HtmlWeb();
web.UseCookies = true;
System.Net.WebProxy wp=new System.Net.WebProxy();
NetworkCredential nc = (NetworkCredential)CredentialCache.DefaultCredentials;
HtmlDocument doc = web.Load("http://www.dsebd.org","GET", wp,nc);
//Set the XPath query
string path = @"//td[@bgcolor='#FFF3E9']";
// Get all columns in the document
HtmlNodeCollection cols = doc.DocumentNode.SelectNodes(path);
Hope this will be useful for you.