Hi Jason - apologies for not posting back earlier.
I think I managed to resolve it - I noticed some difference in some code between the one that worked, and the one that didn't, and changed:
<?php
if (ValidatedField('registration10','registration10')) {
if ((strpos((",".ValidatedField("registration10","registration10").","), "," . "3" . ",") !== false || "3" == "") || (strpos((",".ValidatedField("registration10","registration10").","), "," . "3" . ",") !== false || "3" == "")) {
if (!(false)) {
?>
to
<?php
if (ValidatedField('registration10','registration10')) {
if ((strpos((",".ValidatedField("registration10","registration10").","), "," . "5" . ",") !== false || "5" == "")) {
if (!(false)) {
?>
Which seemed to fix it.
Somewhere along the way, one of my log in pages now no longer works though...
See adjacent thread...