Communicator could not retrieve calendar or Out of Office information from Exchange Web Services. (OCS 2007 R2)

Azurrus used Ask the Experts™
We are currently testing OCS 2007 R2, with Outlook 2007 and Exchange 2007. We also have a couple clients using Outlook 2010. We are using a self-signed cert from an internal certificate authority, which is standalone and not integrated with our AD.

Presence, IM, Conferencing, etc. all work fine for all clients, although the Outlook Busy/Free status and availability when people were in meetings or appointments isn't updating to the Communicator status correctly. Our machines running Outlook 2010 (just two) work fine after manually installing the OCS server cert on the client, but the Outlook 2007 clients this doesn't work.

The screenshots show the status of one of the 2007 clients that is having the problem. It shows a MAPI error. The two Outlook 2010 clients show "MAPI Ok".

From what I understand, shouldn't the Communicator be using Exchange Web Services anyway?
I have already troubleshooted as much as I can. Any other troubleshooting steps would be helpful.
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This was solved.

The reason why this was happening is because we use a self-signed certificate for our Exchange 2007 internal communication. These certs were not installed as Trusted Authorities by our test clients, but they were on our Outlook 2010 clients.

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