Forum Moderators: phranque
That is strange. Make sure your domain name is set up properly, i.e. that the www subdomain is set to resolve to your main domain. Also, it looks like you have a typo in your post... you don't really mean that mydomain/page.html works, i.e. without the .com?
Maybe you could post more detail about the situation such as what web server software you're using (Apache, IIS, ...).