RPC Connection not working on one Exchange server

Hi everyone,

I have this ongoing issue on which I have hit a wall..

I have the following environment

Site A = 1 Exchange server 2010 CAS/MB --> SiteA-Exch2010
Site B = 1 Exchange server 2010 CAS/MB --> SiteB-Exch2010

Both Exchange servers are setup in a DAG.

CAS Array setup with Round-Robin Dns. (Using two CNAME entries)

Client Running Outlook 2010 connected to SiteB LAN.

Here is the issue I experience

If the Mailbox is hosted in SiteA and the CAS Array is resolved in SiteA, Outlook connects fine.
If the Mailbox is hosted in SiteB and the CAS Array is resolved in SiteB, Outlook connects fine.

If the Mailbox is hosted in SiteB and the CAS Array is resolved in SiteA, Outlook cannot connect.
Outlooks displays the following error: "Cannot open your default e-mail folders. Your profile is not configured (/o=company/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=Servers/cn=casarray.company.com)".

In all 3 scenarios, OWA works just fine, therefore only Outlook is acting wierd.

If I use an outlook in SiteA and try to open the mailbox, I have the exact same result as above, but I have a different error in Outlook: "Cannot open your default e-mail folders. The file C:\Users\AccountName\Appdata\Local\Microsoft\Outlook\Account_Email@company.com.ost is not and Outlook data file (.ost)."

I have looked at the RPC logs of the SiteA CAS and I do see incoming connections

I have the exact same entries when CAS Array resolves to SiteB (looking at SiteB's RPC Logs)

I have no idea where to look at now. Any insight would be appreciated.

Thanks