DB_cart class Based on version 1.13 ERROR

Hi i have this error message

Fatal error: session_start() [<a href='function.session-start'>function.session-start</a>]: Failed to initialize storage module: user (path: /tmp) in /clientdata/clients/e/x/express-knowledge.com.au/www/classes/db_cart/db_cart_class.php on line 27


which i don't understand from file db_cart_class.php
I notice that i get it from this code below

if (!session_id()) session_start();

If i comment that code out it'll be fine

This is not a problem of the class or the php code, but a misconfiguration of php in your server.

Try to contact your host regarding this problem.

i thought it might be something ot do with the server configuration.  Thanks for your help.