Call to a member function get_cart_subtotal() on a non-object in config-woocommerce/config.php on line 790

i'm trying t login into my website and this the error that i'm getting while trying to login into wp-admin

Call to a member function get_cart_subtotal() on a non-object in /home/spicom/public_html/http://ift.tt/1XrhWON on line 790

this is my code at line 790

$cart_subtotal = $woocommerce->cart->get_cart_subtotal();

any help guys please ?

via Chebli Mohamed