Thanks to Raffaele, it has been noted that the registration process through the forum was not working properly.

It always gave an error regarding get_error() and sabre. Sabre was the plugin that provided the captcha picture required for registration.

Since there is still a mathematical question, Sabre has been removed.

Registration through the forum (provided by Simple:Press Forum) now works along with the registration through the link down the very bottom right of each page.