Hi Matt,
Our CTO,
NickJ, is well versed with the
mod_security, web application firewall. He'd be able to get this sorted for you once he's back. Meanwhile could you please open up a ticket with the appropriate details to produce the error on our end. We'd be glad to that you're sticking to the security for your website, rather than getting it removed in order to get the form working.. I like people who adhere to security
Good luck..