I have the same issue. I have several images in a gallery and they display fine. It’s only the thumbnails that are not being generated.
When I manage a gallery, I can select an image and set the action to generate thumbnail. The ID 4 error then occurs and no thumb is generated. I don’t think it’s a browser issue as I’ve seen it in Chrome, Firefox, Flock and IE (all latest versions).
It appears to be a server problem.