jquery menu plugin doesn´t work in IE8

jquery menu plugin doesn´t work in IE8

Sorry for my english, I hope I can explain my problem.
I contained a jquery menu from this site: http://apycom.com/  into one of my first projects which you can see here: http://www.lernberatung-karlsruhe.de/index1.html

It works great in firefox, but not in IE6 and IE8?

Here you can see the stylesheet information: http://www.lernberatung-karlsruhe.de/stylesheet.css

Any Idea???
Thx!