The reCAPTCHA wasn't entered correctly. Go back and try it again.(reCAPTCHA said: incorrect-captcha-sol)

Hello, I get only this message: The reCAPTCHA wasn't entered correctly. Go back and try it again.(reCAPTCHA said: incorrect-captcha-sol), although I definitely type in the correct words. Any idea, why is that? Thank you. -- 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://bit.ly/1dkFnYd. For more options, visit http://bit.ly/P65DvS.