guest users

Hello
I install a new plugins ,Contribution and guest users.. and I have an error when
using ReCaptcha,

The form give these error

Please verify you're a human
Input error: Invalid referer

In the panel of configuration of guest user I use

allow open registration : yes

allow instant access : yes

requiere repcaptcha: yes

Thanks
gus

Sorry
but I don't remember see these
https://www.google.com/recaptcha/intro/index.html

gus

Do you have reCaptcha keys set up under Settings > Security?