I got the same problem like him in this thread:
With Firefox and IE9 there is no problem and I can hover the menu and can click on every topic. With IE8 it does not work. If I hover a menu which has a submenu, the submenu disappears when I try to reach a topic in it. In the other thread the admin said to change the class name of the main menu, but I really don't know what I have to do :(
Please can somebody help?