There are some possible causes for this error.

1) You have an invalid domain defined for Simple Survey in the reCAPTCHA developer console, or it does not contain the .secure part on the URL.

You would need to make sure that the address in the Setup Wizard defined here:



Matches the one defined in the reCAPTCHA developer console: 



2) The error could also occur because the following setting is enabled in the Simple Survey Force.com Site in your Org, which makes your landing page secure, but you don't have the domain defined in the reCAPTCHA developer console reflecting the secure link as in step 1.
 


3) As a last resort, make sure that step 1 is complete. Then you can define new Site and Secret Keys and update them in the Simple Survey Setup Wizard.