Unable to add reference to external project

I have this very simple setup.
I created, with MonoDevelop, a new Solution .Net Version 3.5. Added a class within the namespace GameLogic. I build this project, again in MonoDevelop, and it spouts out a dll file.

Then I go into the solution that got created by unity. I add a reference to this dll. I see the reference in the reference list.

I go into a behavour class and write

using GameLogic;

MonoDevelop complains that it can not find this namespace and it also does not compile. Now what do I have to tell MonoDevelop to behave like a reasonable compilersuite.

 

I guess you'll have to add you dll to the Assets folder of you Unity project.