A real CSS mystery

I try to include an ad into my header. With this in index.php:

div id="topbanner" class="column span-14">   <!-- start top banner -->
           <div class="pagetitle column span-5">    // index  </div>
           <div class="column span-9 last"> <img src="images/bg/ad_468-70.png" alt="Nothing visual" /> </div>
        </div>   <!-- end top banner -->

But noet even the alternate text shows up.
Here is the related css:

#topbanner { height: 70px; border-bottom: 1px solid #999; background: url(images/bg/home_banner.png) no-repeat; }
#topbanner_arch { height: 70px; border-bottom: 1px solid #999; background: url(images/bg/archive_banner.png) no-repeat; }
#topbanner_single { height: 70px; border-bottom: 1px solid #999; background: url(images/bg/single_banner.png) no-repeat; }
#topbanner .pagetitle, #topbanner_arch .pagetitle, #topbanner_single .pagetitle { float: left; background: #fff; color: #000; font: 700 2em arial, sans-serif; text-transform: lowercase; letter-spacing: -0.036em; padding: 1px 5px 1px 0; margin: 20px 0 0 0; }

The ad which are supposed to appear in the right div are just not there. Not even the alterante text. Any ideas out there?
Oh, this is a slight mod of The Morning After theme,