Somehow, the server is sending some bad data to ZCO for the appointment whose id is 9438. [The log file had an HTTP 12152 error which indicates this. ]
You can find out which appointment that is in a browser by doing (replace yourserver and yourport):
http://yourserver:yourport/service/c...=9438&fmt=sync
Maybe get rid of that appointment. Before you do, you should do a Show Original on it in the Web client and post it here to see if I can repro.