tfenster2: The reason that line is showing up is because there is an <hr /> element inside your <div id="titlegraphic"> element. While it is not officially in the Style Guide. Other elements, aside from the <h1> that is supposed to be used to display the title of the site, have not been styled and are unsupported.
That means that if you put anything other than an <h1> inside the titlegraphic the result will probably be unexpected. Thus, you will need to either remove the content or put it in the #maincontent.