How can I refer to a project from another one in c#?

Question

I added a project, Project2, to my solution. It already had another project lets say Project 1. How can I call classes and methods from project2 into project1?

What

Answer 1

I had the same problem with this error. I couldn't detect project1 from project2. I had added reference from project2 to project1 but it still didn't work. Then I unloaded project1, removed it from the solution. Then I added it again, made reference from project2 and ta da... it worked..... :-)