I'd successfully run Calendar Server 2.3 on an initial test machine which had an install directory writeable by user 'calendar' - in whose name the caldavd process was run. When I made an install of 2.4 on a beta test machine for which the install directory was not writeable by calendar, I saw the message: exceptions.IOError: [Errno 13] Permission denied: '.../twisted/plugins/dropin.cache.new' (I've elided the actual directory path, as it is not relevant.) The problem is apparently one known in Twisted 8.2.0, which is the basis of the version provided for use with 2.4. See http://twistedmatrix.com/documents/current/core/howto/plugin.html for the background, but I think that the problem is long since fixed in newer versions of Twisted. I worked around the problem by running 2.4 on the initial test system where the install filesystem was writeable before returning to the beta test install. This problem will presumably go away when Calendar Server comes with an up-to-date version of Twisted? John A. Murdie