406 Error (Not Acceptable)
Are you seeing this error when trying to access a page? This is due to Apache mod_security that is turned on by default. While you can use the following to diagnose the problem (turning the filter off should resolve the issue):
It's important to leave the filter on as it helps prevent spam and injection attacks. What you need to do is figure out (ask your hosting provider if you need help) the phrases that are triggering the filter. Typically these will include phrases that include possible commands such as "ftp," "telnet," "ssh," etc. Once you know which ones are, you can modify the filter to permit the page that is not loading (scan your logs or Google sitemap for 406 errors to find all the pages experiencing this problem):
SecFilterSelective "POST_PAYLOAD" "allow these words" "allow,nolog"