DNs forwarding causing login issues.

I am hosting my PHP site from a server at home and have a login issue. I'm using a forwarding service with masking so users don't have to memorize my IP and port number. Here's the deal. If users access my site via forwarding (www.mysite.no-ip.com for example) then they can't log in but if they access my site via it's IP then they can log in. I've noticed that if I turn masking off in the forwarding service that the user can log in no problem, but that is because the url changes to the IP once they get to the site. I've also noticed that as I surf the via masked forwarding site the url doesn't change at all and stays http://www.mysite.no-ip.com. If I surf the site via IP then the url changes as it should (based on the module I'm in, etc).

Anyone have any ideas on what I could do to solve this problem?

Oh. The IP I'm referring to is my WAN. and I'm running on Windoze 2000 Pro, PHP 4.3.5

If everything work fine by IP, it has to be your DNS service. I recommend finding someone else