Adding existing project in c#

I have add the existing project in my new project, but when I try to use the existing library, I see the following error:

t开发者_如何学Che type or namespace name 'com' could not be found (are you missing a using directive or an assembly reference?)

What would cause this?

you must add in your main project reference to other project

(project's property -> add reference -> projects -> select your second project )

or you must add

    using com;

If you have already added the reference to the project then try adding a using for the added class in the .cs file where you want to use it:

using com;

Right click the name of the project you want to add the library to > Select Add Reference, in the dialog box, > select Projects. > Select and ADD the library.

Reference the library in the ‘using’ section of any class you wish to access the library.

using System;
using <nameofproject>

Also read this article.

http://www.csharphelp.com/2006/02/namespaces-in-c/