We set up a "default" project. The Project Settings screen displays "Issue Types [NEW]". And this does not display an Action Drop List, to use for "Use a different scheme"
Ultimately we want to use Sub-Tasks in this project and cannot enable them.
If I create a brand new project from scratch I can easily enable sub-tasks and change the Issue Type Scheme.
Another clue.: Under Settings, Issues, Issue Type Schemes, I see the scheme I want to assign and when I click Associate the drop-down list of projects does NOT contain the project I want to use. So it seems to be a something about that project.
Any ideas?