I get the following error thrown up on several sites when I try to implement Google's ReCaptcha, whether it be using the CB recaptcha plugin, or others:

All of my hosting is done with one provider, I can make two sites using templates from the same company and using the same component, for example RSForm Pro, and I don't get the error on one site but do on the other despite the keys being correct.

Thus far the problem has shown itself in anything I try, for example CB ReCaptcha Plugin, RS Forms, a general ReCaptcha plugin or just inserting the script directly into an article, but like I say I could do this exactly replicated on two different sites and one will work and the other will give this error.

Anyone seen this before and overcome it?