find these lines:
if($signup){
$redirect="$domain/cgi-bin/affiliates.cgi?signup_form=1&adminid=$adminid";
header("Location: $redirect");
exit;
}
and change to:
if($signup){
$redirect="$domain/cgi-bin/affiliates.cgi?signup_form=1&id=$id&adminid=$adminid";
header("Location: $redirect");
exit;
}