I can see one gray image, but have no idea what can be wrong. Have You tried to replace the image ? Maybe it's broken and is rendering like that during thumb creation.
Try also turn off thumb creation and take a look than.
I've checked the article which is having this grey image and looks like you have a one small gray dot attached as article image to this article. So module is working ok. Problem is with K2 which is breaking while I'm trying to upload new image. I've even updated it, but still the same problem. I'm afraid You need to ask K2 developers about this problem, becuase clearly images cannot be added to their component.