We have a BES 4.1.6 with Exchange 6.5 SP2 running and every time a new appointment is added to a calendar on one of the 11 devices we serve I get a CDOCalendar Exception handled. The appointment added on the device was transfered to the exchange server. What causes this error?

What version CDO is installed on exchange?
Are you using ESM and is it up to date via microsoft update (knot windows update)