Sigh... I do not recall making that change but I must've done so! Such a silly, simple little thing has held me back for the best part of a day!
Thanks for that Ray.
As for the persistent checkbox feature, I have this working, so will post it here for my own reference in the future when I struggle with this again... because I will :D :
<?php if (!(strcmp((isset($_GET["invalid"])?ValidatedField("requestcallback","tnc"):""),"1"))) {echo "checked=\"checked\"";} ?>
Once again, thanks for your help on this Ray.
Because you've had a few requests on this reCAPTCHA, I will strip down my page and upload it here for others to use as reference.