How to Fix Uploadify Check Script Not Working

To setup uploadify see the previous post:
Uploadify Setup

To add a check script add the following config:

$('#custom_file_upload').uploadify({
...
'checkScript'   : "uploadifycheck.php",
}

Where uploadifycheck should contain the lines:

 $value) {
  if ($key != 'folder') {    
    $targetFile = $root . "YOUR_PATH" . $value;  
    if (file_exists($targetFile)) {    
      $fileArray[$key] = $value;
    }
  }
}
/* It's important to have these 2 lines, echo or return alone is not enough.
 * If the file does not exists in the web server and you use echo if will not upload.
 * If only return the file will also not upload.
 */
echo json_encode($fileArray);
return json_encode($fileArray);
?>