DHOST doesn't support global variables, thus you must include POST (aka HTTP_POST_VARS) or GET (aka HTTP_GET_VARS) on variables that are passed to other scripts.

$_POST['variable'] - Variables that are directly sent to same/other script.
$_GET['variable'] - Variables passed over the URL. (i.e. script.php?action=go)

If you don't want to have the hassle of adding POST or GET to all of your variables...add this to the very top of your php script:

extract($_POST);
extract($_GET);

That code turns $_POST['variable'] and $_GET['variable'] into $variable. But please note: It's not a very good idea to do this (unsafe).