Test-Webservicesconnectivity Issues Exchange 2010

I have an Exchange environment with 2 sites.  Each site has its own Mailbox and Client Access server the Mailbox DBs are in a DAG between the 2 sites.

I have run the "New-TestCasConnectivityUser.ps1" script from each mailbox server and it successfully creates 2 unique accounts and mailboxes.  From the CAS in SITE1 I run theTest-Webservicesconnectivity -LightMode:$True -AllowUnsecureAccess:$true | fl

I verify that it is successful with the ext_xxxx account created from the Mailbox server in that site.

Now when I do the same thing from the CAS in SITE2 it fails with the error below.  Interestingly enough if I add the switch "-mailboxcredential (get-credential domain\extest_c64c3c75c94b4)" and then pop in the password it works fine.  I have used AD to reset the password to what I know works and also re-ran the .ps1 script that created the account to edit and put in the right password.  If I add the -mailboxserver site2-MB-01 to the command it still issues the same error as below.

Any thoughts on why this isn't working without explicitly passing credentials?  I want to have SCOM 2012 monitor this which is why I need it to work without passing credentials explicitly.

[Microsoft.Exchange.Monitoring.CasHealthStorageErrorException]: An error occurred while t
rying to access mailbox site1-MB-01.domain.local, on behalf of user domain\extest
_c64c3c75c94b4

   Additional information:
   [Microsoft.Exchange.Data.Storage.WrongServerException]: The user and the mailbox are in
  different Active Directory sites..