The error 406 message is a mod_security error. This means the URL you are visiting match with an exploit, hacking or any other attack attempt url pattern based in the mod_security rules we have in the server.
If this is happening in a script you have installed like Wordpress, joomla, etc. please contact the script support for more details.
If you have a custom coded web site most probably your developer used non standard URL variables or formatting which match with a mod_security rule. If you wish to know exactly which is being blocked please open a support ticket.
For more information about mod_security protection please visit the following link: