Internal Error Occured

I just installed this plugin to my site and when I enable the captcha with the keys from google I get the following message :

An internal error occurred: 514513B979E61.A6B8A12.AE00339E

If I disable the captcha, it works, but I’d prefer to keep that for spam prevention purposes..

https://wordpress.org/plugins/clean-and-simple-contact-form-by-meg-nicholas/