This isn’t an “error” message; it’s a totally normal situation. That message is saying “hey, other people pushed new work to that repository while you were doing your work, you should probably integrate theirs into your so they don’t have to integrate yours into theirs?”
So first do a:
hg pull
and then a:
hg merge
Incidentally the revert you did if you actually used the hg revert command didn’t remove those files from history, so your history is probably pretty big.
Consider reading the first few chapters of the Mercurial book it covers these situations quite well.