in the server validation, you have the wrong name for the captcha session.
the code that creates the captcha image:
<img src="webassist/captcha/wavt_captchasecurityimages.php?field=captcha_2&font=fonts/MOM_T___.TTF" alt="Security Code" class="Captcha" />
uses the filed URL variable as the captcha session name. the naming convention is:
captcha_<FieldURL Variable>
in the code, the url variable is:
field=captcha_2
so the name of the captcha session will be:
captcha_captcha_2
change line 17:
$WAFV_Errors .= WAValidateLE((strtolower(isset($_POST["captcha"])?$_POST["captcha"]:"")) . "",((isset($_SESSION["captcha_captcha"]))?strtolower($_SESSION["captcha_captcha"]):"") . "",true,6);
to:
$WAFV_Errors .= WAValidateLE((strtolower(isset($_POST["captcha"])?$_POST["captcha"]:"")) . "",((isset($_SESSION["captcha_captcha_2"]))?strtolower($_SESSION["captcha_captcha_2"]):"") . "",true,6);