the PP_ECO_PHP.php file is used by Expressed Checkout OPut (ECO) only, not be advanced.
Im not entirely sure that advanced returns the transaction ID.
All of the return values will be in a session.
use:
<pre><?php var_dump($_SESSION); ?></pre>
to write the session contents, and you will be able to see if the transaction id is returned and what the session name is.