Well, are you sure it's not your browser? Your thumbnails are showing fine on my end -- if we're referring to the same thing.
I'm not familiar with this plugin in particular, but I think I can probably help. You may have to manually clear your cache from your browser instead of just using ccleaner or whatever. In FF, that means going to tools > options > advanced tab > clear now.
Anyway, this is what I'm seeing:
Healthy Mama Screenshot. But if you want this in your sidebar, then just forget this screenshot.
Let me know exactly what you're trying to accomplish, and I'll take a look at this plugin, download it and put it on one of my WP blogs to tinker with it.
It appears that you want a featured post or two to appear in your right sidebar, though?
I can be easier reached on FB .... fb.me/jasonpaulweber. It's almost always open. That way, we can talk 'on the fly'.