First and foremost, this tool is a HACK. It is offered without guarentee or support! It modifies files generally considered private to the docker daemon!
Docker 1.12-rc3 introduced a breaking change from docker 1.12-rc2. Breaking changes are fully expected between pre-release versions (such as rc2 to rc3 here). However in some cases it can be painful. In this case to fix the comaptability problem you either need to re-create all your containers or manually update the container configuration on disk.
See docker/docker#24343 for more details on the issue. If you do not see the error reported by the original poster, this tool will not help you
This tool will manually update all the container configurations on your docker host so that you won't see this error again.
Once this tool is run you must restart docker.
docker112rc3-runtimefix on your docker host file passing in the path to the containers directory for docker
$ ./docker112rc3-runtimefix /var/lib/docker
Alternatively using the minimal docker image:
$ docker run --rm -v /var/lib/docker:/docker cpuguy83/docker112rc3-runtimefix:rc3
Then restart docker.