Unknown parent error in Mercurial

Try running hg verify on your repository and see if that helps.

I am having the same problem but in my case hg verify returns no errors. Maybe this will help you:

You could try recloning and reindexing. This will fetch a fresh clone from the remote repository and reindex the repository

Source:

https://answers.atlassian.com/questions/59049/fisheye-cannot-pull-from-mercurial