Themes Keep Going

I’ve created a theme and I upload it, no problems there. However If I upload my page templates using the following :

<?php
/*
Template Name: about
*/
?>
<?php include(TEMPLATEPATH . '/header_about.php'); ?>

No problems yet however, once I go and edit one of the page’s to load the above template it does not work, but also the template gets removed from wordpress and so do the other two templates (the default and classic) so I have none installed / able to select in the admin.

I have tried a reinstall over and over yet the same problems it only happens when I load the new headers

This is WordPress version 2.6.2.

Please help many thanks