Thank you for your answer.
I had installed a Prestashop addon for adding captcha on various forms, including the registration form.
But somehow, the captcha does not work any more on the registration form. But it works fine in the contact form and in the login form. So, i disabled it on the registration form, so as users can register. I am talking about Prestashop 1.5.6.2. But i will try to find out why it stopped working on the registration form.
When you say, you have updated the registration form, you mean you have added your self captcha protection without using an add-on ? Or you mean some kind of another protective measure ?
Thank you again!
John