I keep getting the error message and tried like 20x

I've set up the Recaptcha before, and it was pretty easy.I'm implementing it on another web site and I keep getting this error, "The reCAPTCHA wasn't entered correctly. Go back and try it again.(reCAPTCHA said: incorrect-captcha-sol)"I've entered the Captcha like 20x, so it should work.How should I trouble shoot this? -- You received this message because you are subscribed to the Google Groups "reCAPTCHA" group. To unsubscribe from this group and stop receiving emails from it, send an email to recaptcha+unsubscribe@googlegroups.com. To post to this group, send email to recaptcha@googlegroups.com. Visit this group at http://groups.google.com/group/recaptcha. For more options, visit https://groups.google.com/groups/opt_out.