Note: SUPEE-10266 for Magento Commerce (Enterprise Edition) includes a fix for a functional issues MPERF-9685, related to checkout with a zero order amount. This fix is not included in release 220.127.116.11. However, in some cases, SUPEE-10266 can cause issues in the checkout process. Specifically, if a customer enables the Add gift options checkbox during checkout, the checkout process will not progress beyond the payments step. Magento released a fix for this issue as a new patch SUPEE-10384, that needs to be installed on top of SUPEE-10266.