As others have suggested, that white band is meant to be there. It should display an advert but, for some reason the box is loading but the advert itself isn't. Closing an ad there (or, in your case, the absence of an ad there) simply results in it being replaced by another ad (or, for you, just another blank box) shortly afterwards.
Something in the settings of either your browser or your security software is probably preventing the ads from loading but (unless you're desperate to see the ads) there's probably not much point trying to identify the relevant setting. You'll still see something (whether it be an ad or just a white box) at the foot of your screen. It's simply part of the way that AB works; you just have to scroll the page to read the bit that you want to see.