Thanks for the quick reply. Do you know specifically what the issue with mod_security is and why the word "board" would break it?

Strange one this, any time I attempt to put the word "board" into a post, I get a 403 Forbidden error:

"You don't have permission to access /forums/post.php on this server."

This is also preventing me from changing any admin options, as when I try to submit the form I get a 403 error, and the word "board" is on the page multiple times, obviously.

Any ideas? I'm running 1.2.16 with the Private Message Mod v 1.2.3.