Top Level Nav Not Working for Some Users

I have had several complaints on a website I designed using a SiteAssist Pro template.
www.nsdtrc-usa.org/

The problem is that the top level navigation bar is dead--no change in color, no links for some users. The fly out menus work fine for them. When I test the menu on IE, Firefox, and Safari everything works fine for me so I'm not sure what the issue is for these people. From what I've been able to ascertain, these people are using newer versions of IE as their browser. I do not know if they have js disabled, but that doesn't make sense to me since the fly outs work.

Do you have any suggestions?

I tested the site out in IE6, 7 and 8, FireFox 3, Chrome, and Opera. They all seemed pretty good except for Opera. It looked like the menu css was all messed up there. This might be a good question to ask anyone that is reporting the issue. I also noticed that there was a newer version of Opera available but I did not try it out.

Thank you for testing the site. I am at a complete loss on what to tell these people since their expectation is for me to "fix" a problem that I can't replicate.

One thing you can ask them to try is to use a different computer for testing to see if it occurs there as well. Also have them test different browsers as well. Also ask them if its an intermittent issue or if it happens every single time. Try having them clear the cache and then viewing the page again.