Internal Server Error 500 - Entering Products

[Trinity]

I have a new installation of 1.3.9.

When I try to add products I get an Internal Server Error 500

I have checked the server log and found this;

[18-Nov-2010 07:32:34] PHP Fatal error: Call to a member function get_template_part() on a non-object in /home/xxxxxx/public_html/index.php on line 29

Any ideas what this is? I checked the line in index.php and it is:

$directory_array = $template->get_template_part($code_page_directory, '/^header_php/');

Any ideas, my knowledge of PHP is only very basic.

Thanks in advance. :-)