In case there are any errors after upgrade, please go through the following checklist: * Are template/skin/layout files from latest version really being used ? Old files may be used from theme folder. * Some cache may need to been flushed. If you are using APC/XCache/OPCache, check if new files are really used * Check One Step Checkout page source and in case there are multiple jquery imports, remove all except one. If jquery is included more than 1 time, it breaks scripts. You can ignore the One Step Checkout jquery import, it has a if-condition and only gets loaded if jquery has not been loaded before.