Ok guys here it is.
Make sure you use the right path to ssi_in.php
Make sure you have the right "main page" in your admin (index.shtml or index.php)
Make you sure you have the right insert at the top of your main page.
This one works for me
<?php @virtual("/home/me/domains/mysite.net/public_html/tp/tp/ssi_in.php")?>
There is also
<?php virtual("/tp/ssi_in.php")?>
and
<!--#include virtual="/tp/ssi_in.php"-->
Looks like it's all working