A Tremendously Annoying Z-Index Problem

I have a site I’ve worked on, and there is just ONE little problem left on this page:

http://www.madatoms.com/site/writer/most-viewed/all/P0/

If you try to click on Writers and Artists, you can only click on the part of the image that is lower than the main navigation’s background image. Through tinkering, the only solution I’ve found is to make the main navigation’s z-index negative. Even if I make it 1 or 0 and have the subnavigation’s set higher, it doesn’t help.

But if I make the main navigation’s z-index negative, then the main navigation’s links don’t work! None of them! They don’t do anything!

All my code is there if you use view source, the CSS file is at http://madatoms.com/themes/site/css/all.css