Today I booted up my XAMPP install. When I started Apache I got a 324 error. A lot of the Google hits for this showed problems that were specific to browser configuration.

In this case, it was my server configuration. Disabling my Passenger configuration helped; I then started getting 403 (incorrect permissions on the server) errors. The hallmark of this particular problem is seeing a lot of this in your error_log:

client denied by server configuration

Looking back to my config I found I had a virtual host (vhost) configuration on *:80. According to Site with a Lamp a change to Apache adds in

Order deny,allow
Deny from all

Subsequently, in order to allow Apache to serve up ANY files in a directory, you'll need to add

Order allow,deny
Allow from all

Getting rid of my vhost configuration solved the problem and all ran as before. The villagers rejoiced.