It could be a security module installed preventing html code from being posted... I see you are using an html editor and sometimes security is added to a site to prevent html injection that basically prevents html editors from working. I'd ask your hosting provider to see if that is what is going on.
A good test would be to make the editor field blank when submitting and see if the error goes away. That would be a sign that the html in the post is causing the error.
Did this help? Tips are appreciated...
