I have a lot of images. When I try to remove them with docker rmi
$ sudo docker rmi acd33a9490dc
Error response from daemon: No such id: 75ce1f6710b
So... some cases of this seem to be because you have a no-longer-running container that references the image. Removing the container allows you to then remove the image.
But there is definitely a bug where docker gets itself into a state where no matter what you do, it can't remove any image. This has been fixed in docker 1.4.0: https://github.com/docker/docker/commit/ac40e7c