Comment Spam Pack - Custom Anti Spam not blocking spam

Hello - I've added the Comment Spam Pack to my site but the Custom Anti Spam plugin isn't working at all. Tested on IE, FF and Chrome - both logged in and logged out - it allows me to post a comment without putting anything in the captcha form. Even if I type a random message in the form, it's still posting.

Can someone confirm that this plugin works as expected and maybe point me in the direction as to what I'm doing wrong?

cheers!
dale