Okay, I found the source of the problem on my own. The only thing that really helped was some discussion in Bug 27683 which suggesting looking at Outlook add-ins.
The copies of Outlook which we were using had previously been tested using the Communigate Pro MAPI Connector. Even though this connector was not being used within the Zimbra Outlook profile, it was interfering in some way with ZCO.
The following steps solved the problem:
1. Quit Outlook.
2. Delete the profile associated with the Communigate MAPI connector.
3. Run the Communigate Pro MAPI connector installer and select the Uninstall option.
4. Launch Outlook.
(By the way, OL 2007 has moved the add-ins manager to "Tools...Trust Center", although I didn't actually look there until after the problem was fixed, so I don't know if the Communigate Pro Connector would have shown up there.) |