I was getting this error when trying to use Tailor with Mercurial on Leopard:

Common base for tailor exceptions: 'hg' is not a known VCS kind: No module named mercurial

Mercurial was installed, so the error mystified me. Turns out to be a problem with python versions in use. Leopard's python is version 2.5.1, but mercurial from MacPorts depends on python 2.4, and so MacPorts installs python24. So when running tailor with python 2.5 and trying to load the mercurial module which is installed for 2.4, not 2.5, it naturally fails. The workaround is to run tailor with python 2.4 instead, which works fine.

#! /bin/sh
# Save as ~/bin/tailor and chmod +x
tailor=$HOME/src/tailor/tailor
exec python2.4 $tailor