Form submits even with validation applied

Hello,

I have recently inserted captcha security on a form that we have created, applied server validation and created an error message if an error occurs. We attempt to generate an error but the form submits.
Not sure if this is a problem however, we are using gdform.php script for the form:
<?php
$request_method = $_SERVER["REQUEST_METHOD"];
if($request_method == "GET"){
$query_vars = $_GET;
} elseif ($request_method == "POST"){
$query_vars = $_POST;
}
reset($query_vars);
$t = date("U");

$file = $_SERVER['DOCUMENT_ROOT'] . "/../data/gdform_" . $t;
$fp = fopen($file,"w");
while (list ($key, $val) = each ($query_vars)) {
fputs($fp,"<GDFORM_VARIABLE NAME=$key START>\n");
fputs($fp,"$val\n");
fputs($fp,"<GDFORM_VARIABLE NAME=$key END>\n");
if ($key == "redirect") { $landing_page = $val;}
}
fclose($fp);
if ($landing_page != ""){
header("Location: http://".$_SERVER["HTTP_HOST"]."/$landing_page");
} else {
header("Location: http://".$_SERVER["HTTP_HOST"]."/");
}


?>

Not sure why this isn't working??? Any help is greatly appreciated.

Thanks,

Jackie

I've also attached the files, if that helps.