We have a BES running on Windows 2003 server, version 4.0.0.110 and we are getting a lot of strange Calendar errors in our windows event log.

We get a new error every couple of seconds, the source is BlackBerry Messaging Agent (Servername) Agent1

and the error reads..

{Username} CDOCalendar::Initialize - QueryInterface (0x80004002) failed

I've checked the cdo.dll file, and the correct version is registered.

Any ideas?

Looks like you haven't applied any service packs to your BES. I would recommend getting to Service Pack 4, Hotfix 3 at a minimum. SP4 fixes a LOT of calendar issues.

Can service packs just be installed right over the existing install? The only guides I was able to find online seemed to treat each service pack as a clean install.

No there two versions out there, one is a clean install and one is an udate version. For the update look at the installation guide there is an upgrading section.

Yes you can directly apply service packs 4 or 5
Service Packs are Cumulitive unile HF's which are incremetal.

I suggest go directly to SP-5

For your problem ,also check the Servcice account permissions on the Mailbox stores and the Public Folder stores