Thanks, but that's just XenForo's generic error message--it can be caused by just about anything. The underlying cause in that thread was ModSecurity + cPanel, but NamePros doesn't use ModSecurity (or cPanel, or Apache).
Unlike vanilla XenForo, NamePros logs most user-facing errors, even if they're expected. For example, if you try to post a thread but receive an error message indicating that you're not allowed to post links, we log that. If you subsequently contact support, the tech team can pull up those error messages along with technical details that could help identify any problems on our end.
In this case, no relevant error messages were logged, which is concerning. Any additional information about the incident would be helpful. For example, did the message eventually go through on a subsequent attempt? Was there something in the message that might've looked like spam to our system?
NamePros is relatively big for a PHP-based website, especially one running XenForo--certainly not the biggest, but big enough that we're often navigating uncharted territory. It's not unusual for us to encounter all manner of obscure bugs. Our dev team is no stranger to debugging these, but the first step is always getting as much context as we can.