Beagle has this nasty problem for me. When beagled starts this happens:

Debug: Getting calendar changes for file:///home/nigel/.evolution/calendar/local/system
Error: Unhandled exception thrown.  Exiting immediately.
Error: GLib.GException: Unknown error
in <0x00187> Evolution.Cal:GetChanges (string,Evolution.CalComponent[]&,Evolution.CalComponent[]&,string[]&)
in [0x0003f] (at /tmp/buildd/beagle-0.2.4/beagled/EvolutionDataServerQueryable/CalContainer.cs:92) Beagle.Daemon.EvolutionDataServerQueryable.CalContainer:IndexChanges ()

I'm not sure how to actually fix it, but a work around was found here, which basically equates to: apt-get remove beagle-backend-evolution