CAPTCHA session reuse attack detected error message when form is submitted

I am experiencing problems with the captcha module 7.x-1.0-beta1 version. I have enabled captcha in webforms for anonymous users. After submitting the form it repeatedly gives me the error message, CAPTCHA session reuse attack detected.. This happens for only one of the webform in which captcha is placed. I am using Drupal 7.2 version.

Any solution for this issue will be really helpful.