Visual Studio 2015 not recognizing references

Question

I have a solution with some projects. I am in project 23 and I added a reference to project 5, but Visual Studio does not recognize any class from project 5 nor the project 5. I tried using _05. Nothing works. Am I doing something wrong?

Answer 1

Classes in 05 should be public.

public class Ejerkikio_05
{
....