Fatal error

Hello,

i get this error when i tried to active this plugin

Fatal error: Class ‘WC_Payment_Gateway’ not found in /home/XXX/public_html/wp-content/plugins/sagepay-direct-for-woocommerce-payment-gateway/ds-sagepay-direct.php on line 109

My WordPress 3.4.2 and
WooCommerce Version 1.3.2.1

Thank you
M

http://wordpress.org/extend/plugins/sagepay-direct-for-woocommerce-payment-gateway/