Steps to reproduce

1. Create private Mercurial repository (for example use Bitbucket.org)
2. Checkout repository to some folder
3. Install Mercurial 3.8.4
4. Add local repository to SourceTree
5. Try to pull changes from SourceTree UI

Actual result: After some waiting error message "abort: authorization failed" is shown;

Expected result: Changes are pulled without errors;
Also expected result: Error messages should notice that Mercurial version 3.8.4 and older are not supported.

This situation happened when I updated SourceTree and not updated Mercurial for a long time. Even when I use embedded Mercurial. Workaround is to update mercurial (Embedded or System) but error message doesn't explain that.