Look through src/or/connection.c for "Directory unavailable". This
happens when you try to ask for a v1-style directory object (either
a full directory or a running-routers list), and the directory mirror
doesn't have a suitable copy yet.
Most commonly this is because the server just started and hasn't found
a copy it likes yet.
With more and more Tor servers upgrading to 0.1.2.x and later, it will
become increasingly rare to find copies of the v1 directory objects (since
they will decline to serve them more often, sending a "503 Directory busy,
try again later").