Getting HTML from a page behind a login

Question

This question is a follow up to my previous question about getting the HTML from an ASPX page. I decided to try using the webclient object, but the problem is that I get the

Answer 1

Well does opening the page in a brower with "Login.aspx?UserName=&Password=" normaly work?
Some pages may not allow login using data provided in the url, and that it must be entered in the login form on the page and then submitted.

Answer 2

The only other reason I can think of then is that the web page is intentionally blocking it from loggin in. If you have access to the code, take a look at the loggin system used to see if theres anything designed to block such logins.