Alternate Access Mapping Problem

Hi,

I created a Web App and added a DNS Host Record and did the IIS Binding for the Site. I have a site collection for which the Domain Administrator is the Primary Site collection Administrator.  But when I try to access the site IE gives the Windows security Login form. It wont let me in after entering the credentials. The url is added into the browser trusted zone, But still cant get past the security login form.

Any idea what the problem could be?