Woocommerce troubles..

What does this mean..

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘woocommerce_price_filter’ not found or invalid function name in /home/npssanda/public_html/wp-includes/plugin.php on line 199

Warning: array_unique() expects parameter 1 to be array, null given in /home/npssanda/public_html/wp-content/plugins/woocommerce/includes/class-wc-query.php on line 353