You need to check also the Project
tab on that page, and each module's SDK under the Modules
tab and its Dependencies
sub-tab. They all allow you to specify what SDK to use at different levels. The Project
tab should be set to the only SDK you have, but it might not have anything set and similarly for the module dependencies - they should be set to 'use Project SDK' but they might not be. That's usually the source of the kind of error you're seeing.