Checking out tags suddenly complains of local changes and Aborts.

[pjakobsen]

git checkout chapter5-2
error: Your local changes to the following files would be overwritten by checkout:
.meteor/packages
.meteor/versions
Please, commit your changes or stash them before you can switch branches.
Aborting

[SachaG]

This means you need to commit your changes or stash them with git stash.