Unable to reference SmartFTP Library

Hi Team,
I am using SmartFTP 1.5 Library in my project and have come across some issue. While referencing the library in the project, I am getting the error as '<The system cannot find the reference specified>'.
The project where I am trying to reference is a simple VB.Net Class Library project.
Any help in this regard is greatly appreciated.

Version 1.5 is no longer supported. Please upgrade to the latest version.