I'd finished my first module and its Windows Form Application. It contains 5 forms and those forms calling each other (Form1.Show, Form2.Show, Form3.Show) something like that. But then knowing in my professor that it should be an Class Library Application Type. When my professor try to integrate it in the main application. Now all referencing forms where underlined as error. I can't call the form2, nor form3. What should i do ?