[biocyberman]

I got the same problem after moving my forum root folder to a different unix account. Firefox error console says

Error: The stylesheet http://<path_to_my_forum_root/clientscript/vbulletin_css/style0009l/forumbits.css,forumhome.css,widgets.css,sidebar.css,option.css,tagcloud.css was not loaded because its MIME type, "text/html", is not "text/css"

This is a strange error. I took a look at one of the css files in the list in the error. I noticed strange things: for example, in forumbits.css the urls are wrong:

.forumhead{background:#FFF url(http://<my_old_url>/images/buttons/newbtn_middle.png)

From here I found my solution:

1. Change owner of the clientscript/vbulletin_css to that of web server
2. In vbulletin control panel, search in template, find forumbits.css by name. Open it and save. This is just to trigger vbulletin to update css files under clientscript/vbulletin_css
3. Problem solved.

It wasted 2 hours of my time, +++++ing and swearing