Project Structure (Unity game / Visual Studio Solution / ODIN Serializer)

Hi there. I am working on a basic 3D puzzle game made with Unity 5.3 and VS Community 2015. I target Android (mobile and tablet) as well as Windows 10 (PC) The value of my game resides in the mechanics but moreover on the puzzles, that are unique and involves intricate design (maths) For that matter, I would need to encrypt the puzzle data, with Odin Serializer for example Then to summarize, I have my Unity game, a VS 2015 App that generates the Puzzle encrypted data, the database itself (or several versions for free to play and IAP) attached to a class library (data) that would be accessed from both the Unity game and the Puzzle Generator application (see picture)![alt text][1]

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My Old Project, Still Moving Forward, Still Alive #X100309

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Problem is, every time I try to declare references to the DLLs, I get an error : "unable to add a reference to project "Odin Serializer", the same to add the Class Library (data) to the Puzzle generator app. What is going wrong here ? Wrong project type ? Wrong Microsoft Framework ? Thanks in advance for advice.