If the reason you can't click the link is because the link disappears before you get a chance to click on it, then the reason (in IE) is because of the gap between level-1 items and level-2 items.
You can fix this by closing that gap by adjusting the 'left' rule in your menu.css file at line 146. Try changing:
ul#cssmw_home ul.level-2 {
left:170px;
padding-left:5px;
}
to:
ul#cssmw_home ul.level-2 {
left:165px;
padding-left:5px;
}
If the gap problem also occurs when you move the mouse betweedn level-0 and level-1, you would need to remove or reduce the 7px 'padding-top' value from around line 89:
ul#cssmw_home ul.level-1 {
left:0;
padding-top:7px; /*remove or reduce this value */
top:100%;
}