The template upgrade feature is enabled as a parameter in Ariba but it's also a feature in the template Advanced tab. There are 3 levels for the parameter: No upgrade, Ask When Upgrade, and Upgrade Automatically. If you don't have any assembled documents, then you can use the upgrade automatically setting. Otherwise, you will need to use the "ask" setting. This is important when you have a mixed template environment, some with assembled documents and some not.
When the "ask" feature is enabled and the user selects Amend, they are presented with a radio button yes/no defaulted to no. They will need to select Yes to get the upgrade. Obviously, sometimes this will be missed.
If you have an assembled document and either use Upgrade Automatically or if you select Yes to the ask question, and your template is set to upgrade, you will get an error.