It means that the server only allows you to clone branches and tags, not individual commits which are not on a branch or tag. (more specifically, it only allows you to fetch what it has told you in the beginning exists)
If that happens, one can just clone the latest branch or tag without depth restriction (which means it will clone the ENTIRE repository) and then git checkout the commit you want. That's a major reason why I put a fallback in our git-download module. I don't know what the benefit of the restriction is, though.
pgpmXrp2F5eA4.pgp
Description: OpenPGP digital signature
