Error occured building Repetier-Host Plugin, what should I do?

I`m a beginner level in C#.

I want to make my custom plugin for Repetier-Host.

I downloaded DemoPlugin.zip in this site https://rhplugins.repetier.com/ for testing,

build using Visual Studio 2019.

But error occured like picture, but I don`t know what should I do.

Please Help me..

My Repetier-Host path is "C:\Users\admin\Desktop\Repetier-Host"