Mercurial hg Subrepository issue - "abort: unknown revision'

I'd guess the .hgsubstate file now contains a hashid (which is what your LongGUIDLookingString is) from repo3 in the repo2 entry.

Try editing .hgsubstate to point to a correct/present hashid for each repo.

If that doesn't work, please paste i your .hgsubstate file so we can see how it can be tweaked.