Error Message while trying to post a message

Hi there, 

When a user tries to post a message in a post, they are getting an error message saying that the configuration can't be change? and does not allow them to post a message or a response. But if I logging as an admin, I can post any messages and responses.-

Also, if I turn off the plugin and use the default WP message and try to type a message I get the below error message. Any suggestions?

Not Acceptable!

An appropriate representation of the requested resource could not be found on this server. This error was generated by Mod_Security.

Thanks, 

Miguel