I've had alot of spambots recently and just checked the registration page and the recaptcha verification is not appearing at all!
I have already searched on forum and checked the following:
Usergroup for Unregistered: must use human verification
Human verification in vbulletin options and checked all the checkboxes (register, post, contact us...)
reuploaded register.php
Also the strange thing is that the verification is working for sendmessage.php (contact us) and when posting as guest but not for registering. I have tried disabling all "hooks" but still no luck.