XF 1.4 White block at bottom of page


I created a new theme for my forum, and it looks fine and covers the page normally, but when I go to a page with less content, I have a big block of white space at the bottom of the page. Like so:

page error.JPG

The background image that I'm using doesn't seem to be the problem because when I add code to have it cover the page, part of the image is obscured by the white block.

I thought this was an HTML problem, but I can't figure it out.