I don't understand you. Please leave your reCAPTCHA settings screenshot. Have you generated and inserted reCAPTCHA API keys? The error says keys are not valid so you've inserted wrong Keys.

yes I inserted the keys !! but I deleted them thinking that I did not have the problem anymore

How i'm doing NOW ?? 

Ok, now. generate it again. Click on this link and generate new API keys:

http://www.google.com/recaptcha/admin

Create new API. Make sure you copy correct key to correct field. make sure you don't insert extra spaces before or after keys.

Help video: https://www.youtube.com/watch?v=q9VD3CQwhi4