WBEM_E_ACCESS_DENIED on Exchange mailbox server (works fine on CAS box)

ZenOss 4.2.3 running on RHEL5.

We have a 2-server Exchange 2007 environment.  Setting the CAS/Hub server up with WMI monitoring was a snap, and the better event logging is keeping us busy but in a good way.  Not so much with the mailbox server.  No matter what server class we set it up with, even just /Server/Windows, still it's logging constantly like this:

Could not read the Windows event log (ExecNotificationQuery on HOSTNAME.domainname.example (WBEM_E_ACCESS_DENIED)). Check your username/password settings and verify network connectivity.

As mentioned earlier, we've tried using all the different classes within the /Server/Windows tree and all result the same.  Further, I've verified that the domain account we use for WMI query activity is a local admin on the Mailbox server.

Here are the steps I performed using wbemtest:

• Logged in to the mailbox server using the WMI query domain account from a remote machine.
• Issued the following query to enumerate all the event logs:
  • Select * from Win32_NTEventLogFile
    
• For each event log returned from the above query, I issued a test query to get any events as follows:
  
  • Select * from Win32_NTLogEvent Where Logfile = 'Filename'
    
    • eg Select * from Win32_NTLogEvent Where Logfile = 'Security'
      

It's worth noting that I did not get WBEM_E_ACCESS_DENIED from any of the above queries.  Since the mailbox server is configured to all intents and purposes the same way as the CAS/Hub box I'm at a loss to explain what's failing or why.

Is there any way to test the actual query Zenoss is running to find out why it's failing?