We were working on a client's website and he reported that, his Joomla regular registration form was not working right and not allowing anyone to register with an error message on the top, "Empty Solution not allowed".
We started looking into it and found out, the culprit was the mis-configuration of the Captcha settings. Here is how to fix this.
- Goto Plugin Manager and Activate Recaptcha Plugin. Enter Private and Public Key for Recaptcha. You can generate them from here
- Goto Global Configuration > Captcha > Select ReCaptcha
- Goto User Manager > Options on the top right of the screen. Enable REGISTRATION and RECAPTCHA from there too.
You are done! Test the registration form on the frontend now.