Access Class Libary from Universal Shared App

i have an Universal Shared Application which contains some Javascript/Html Code. See project structure here:

Now I want to access some native functionality which should be shared among the both projects. I tried to create a "Class Libary (Universal Windows)" and "Class Library Portal for Universal Windows 8.1" but i can't neither of them reference to the Shared App.

"One or more selected items is not a valid reference for this type of project"

What am I missing? What are the restrictions for my intend?

via Chebli Mohamed