Alternate URL not accessable from with in server

Hi,

I am facing issue of Alternate URL is not been accessable from with in server but when access from any system in domain it is accessable.

We have configured alternate access mapping that is working fine else then when the alternet URL is used to access the site from the server where sharepoint is deployed. It ask for credentials and after that only return an empty page.

Explanation:

http://servername/ work fine from with in server and on network

http://sharepoint.porta.com/ work fine on network but when on server empty page is returned.

Thanks in advane

Best Regards, Syed Muhammad Ehsan MCTS SharePoint Server 2007 (Dev & Config)