Your script is 4 years old. I'm sure that things have changed since the original post. The correct url would be http://www.mydomain.com/domains/, not register.php.
Here's the original post.
Good catch of a possibly duplicative posting, but while "choudiandian," a "SitePoint Zealot," joined sitepoint.com four years ago, the question appears to have been posted on 20100605 (at 20:51, TZ unspecified).