Hello!
I have a very odd problem with this plugin. I downloaded it a few days ago. I believe it was Monday or Tuesday this week. And it worked fine then. I tried using it again yesterday and tomorrow again and it just refused to work. I'm running Paint.Net 3.5.11 on a Windows 7 machine.
When I use the Object Outline effect, it just looks like it doesn't do anything. When I zoom in enough, so I can see the individual pixels, I can see that it puts one pixel of the colour I chose for the outline on every few pixels.