Unable to invoke a class in C#

I've tried to invoke an object for a class in the external project in Windows Forms (C#).

using

Somehow, I've added the dll as the reference.
Tried to add the namespace. Unfortunately, I couldn't include the namespace.

Digging the content, I found the real reason for this issue.  The reason is,


1. The class is not declared as public
2. May be the issue is with the namespace.

Cheers,
Venkatesan Prabu .J