Orders not being sent

I really enjoy the plugin. It allows me to offer bulk pricing on products, however, just the other day, I saw an order go through my credit card, but I did not get a confirmation email of the order, nor did the customer.

When I tried to send the order manually, this is what I got:

Fatal error: Uncaught Error: Call to undefined method WC_Order_Item_Product::get_price() in /home1/wahshs0add5a/public_html/wp-content/plugins/woocommerce-fixed-quantity/classes/woofix-utility.php:130 Stack trace: #0 /home1/wahshs0add5a/public_html/wp-content/plugins/woocommerce-fixed-quantity/classes/client-fixed-quantity-price.php(361): WoofixUtility::calculatePrice(Object(WC_Order_Item_Product), 1) #1 /home1/wahshs0add5a/public_html/wp-includes/class-wp-hook.php(288): WooClientFixedQuantity->order_formatted_line_subtotal(‘<span class=”wo…’, Object(WC_Order_Item_Product)) #2 /home1/wahshs0add5a/public_html/wp-includes/plugin.php(208): WP_Hook->apply_filters(‘<span class=”wo…’, Array) #3 /home1/wahshs0add5a/public_html/wp-content/plugins/woocommerce/includes/abstracts/abstract-wc-order.php(1639): apply_filters(‘woocommerce_ord…’, ‘<span class=”wo…’, Object(WC_Order_Item_Product), Object(WC_Order)) #4 /home1/wahshs0add5a/public_html/wp-content/plugins/woocommerce/templates/emails/email-order-items.php(76): WC_Abst in /home1/wahshs0add5a/public_html/wp-content/plugins/woocommerce-fixed-quantity/classes/woofix-utility.php on line 130

I was told by WooCommerce to deactivate the plugin and try again, and it worked. The plugin has been deactivated, but I really want the functionality of offering discounts on bulk orders. Looking forward to your help.

Adam