Still not sure; I need to go do some testing of my own, but can you check on something? I think this line might be a clue:

On Apr 1, 2013, at 1:50 AM, Nikola Knežević <laladelausanne@gmail.com> wrote:

2013-04-01 10:46:39+0200 [-] [caldav-0] [-] /usr/local/caldavd/lib/python2.7/site-packages/Twisted-12.3.0-py2.7-macosx-10.7-intel.egg/twisted/python/util.py:560: exceptions.UserWarning: tried to drop privileges and setuid 93 but uid is already 93; should we be root? Continuing.

Is your SSL cert (including private key & any chain certs) readable by UID 93?

-glyph