PHP CAPTCHA is not validating for some strange reason

I was using PHP CAPTCHA successfully in several of my sites - however, when I tried the same in my new project by copying the files, I found that the validation is not hapenning.

Everything works, the captcha image gets echoed, but on submit,

PhpCaptcha::Validate($_POST['captcha'])

returns false. Any idea what may be going wrong here ?

Thanks for your time guys.

Need to see the rest of the code to have any idea of what it might be. If you add debugging echo() statements does anything stand out to you?