Symptoms

Trying to clone a Mercurial (hg) BitBucket repository with SourceTree results in the following:

This is a Subversion server (must clone to Git or Mercurial)

Cause

The PATH environment variable for the OS X applications set within ~/.MacOSX/environment.plist may have been broken by installing an other application.

Resolution

Update the ~/MacOSX/environment.plist so that it also contains the following:

/usr/bin
/bin
/usr/sbin
/sbin
/usr/local/bin

After altering, you may need to reboot