I have added an error in the
sales_quote_save_before event, if the quantity of items is more than 500.
> Mage::getSingleton('checkout/session')->addError(Mage::helper('checkout')->__('The maximum order qty is %d', 500));
The error appears in the cart, but still I can go further to the checkout and place the order. How can I disable the Proceed to Checkout button?