Mercurial: “untracked file in working directory differs from file in requested revision”?

Question

Can anyone tell me what this Mercurial error means?

untracked file in working directory differs from file in requested revision

Answer 1

I tried Ry4an's answer (of deleting the file) and it still did not work, so I ran a purge and that got rid of all traces such that it worked after. Just in case somebody is looking for an alternative solution.