hmmm, doesn't look like the captcha session is gettting set.
try changing:
<img src="WA_ValidationToolkit/WAVT_CaptchaSecurityImages.php?noisecolor=<?php echo $WAGLOBAL_Captcha_Noise; ?>&bgcolor=<?php echo $WAGLOBAL_Captcha_BG; ?>&textcolor=<?php echo $WAGLOBAL_Captcha_Text; ?>&transparent=<?php echo $WAGLOBAL_Captcha_BG_transparent; ?>&characters=<?php echo $WAGLOBAL_Captcha_Characters; ?>&width=<?php echo $WAGLOBAL_Captcha_Width; ?>&height=<?php echo $WAGLOBAL_Captcha_Height; ?>&font=<?php echo $WAGLOBAL_Captcha_Font; ?>" alt="security code" /><br />
to:
<img src="WA_ValidationToolkit/WAVT_CaptchaSecurityImages.php?field=1&noisecolor=<?php echo $WAGLOBAL_Captcha_Noise; ?>&bgcolor=<?php echo $WAGLOBAL_Captcha_BG; ?>&textcolor=<?php echo $WAGLOBAL_Captcha_Text; ?>&transparent=<?php echo $WAGLOBAL_Captcha_BG_transparent; ?>&characters=<?php echo $WAGLOBAL_Captcha_Characters; ?>&width=<?php echo $WAGLOBAL_Captcha_Width; ?>&height=<?php echo $WAGLOBAL_Captcha_Height; ?>&font=<?php echo $WAGLOBAL_Captcha_Font; ?>" alt="security code" /><br />