CiviCase Will Not Save Settings for Activities
There are a couple of things to look out for.

If you are creating a new case type, we had to delete the default role that is automatically assigned (case coordinator I believe), save and then re-add the role before it would save.

If you are working form the older xml files to configure cases, I'm not sure that the case ui will work with those.  You may have to edit those files manually.