I recently looked at this old gem again and I've noticed the feature that registers and lists server hosts for D2TGP is no longer working for most people. I don't yet have an explanation; the call is coming through as it should be from the game, and the sites it points to are easily accessible by hitting the web address in a browser. My best guess currently is that a recent Windows update that was pushed to almost everyone has changed something in security. If you have any suggestions please post them in the forum.
In the mean time, please be aware that you can easily host games just by giving out your IP address for others to connect to manually (though keep in mind you may still have to open ports 10191 and 10192 on your firewalls as usual).