Today had Leon and I banging our heads against a new WordPress installation that was displaying a blank screen in the visual editor. We searched for possible causes and solutions, which included disabling possibly faulty plugins and verifying that all WordPress files were installed.
In looking more closely at the browser console, what first appeared to be 404 non found errors were actually turned out to be 403 forbidden errors. It seems that our Web server is configured to treat the extra get request (file.css?stuff=something) as something that can be executed, while the css file permissions were set to read-only.
The fix was to set up Permalinks and add an .htaccess file to the rood directory of the WordPress install. While I’m not completely up to speed on what aspect of mod-rewrite fixed the issue, I think it may have expressly directed to treat existing files and directories as files and pass other requests through WordPress. Question is whether it is passing the css file through WordPress, or loading it without the request… Any ideas?