IE7 z-index / 960gs multi-level menu "disappearing" bug

Another week, another problem. I've read all the blogs, and have searched for hours on here, but have not found a working fix.

Here is the site in开发者_运维知识库 question: http://www.opexsvs.com/ (I'd post the code here, but it is quite long and probably has something to do with something farther in the DOM that I'm not noticing).

I'm stumped on the multi-level menu. When you start rolling down the "Services" items in IE7, the menu disappears.

Please let me know if you have a fix for this, all other browsers are behaving properly and I can't seem to debug it in IE7. Thanks!

If anyone is interested in the fix, I got help over on reddit (http://www.reddit.com/r/web_design/comments/ha5j1/anyone_around_that_would_be_able_to_help_me_fix/)