I'm trying to add an internal library to my project using an example from here:
Example of Adding Internal Libraries

I have a minimal Qt Widget Application (created by the creator itself, which is running). Then I added an other project, as said in the example. In step 4 I can not select any project from the list (Add as subproject to project), because it is empty and disabled.

Using the contextmenu of my Widget project, I select 'Add library', then 'Internal library'. In that dialog the dropdown list 'library' is empty, but enabled.

I'm using Qt Creator 4.0.3, Based on Qt 5.7.0 (MSVC 2013, 32 bit), Jul 5 2016 01:09:09.

What am I doing wrong?