Hi,
From your description, I guess that you have run the Get-ActiveSyncVirtualDirectory cmdlet in the addition CAS server. Is it right?
From the link
http://technet.microsoft.com/en-us/library/aa996042(EXCHG.80).aspx , we can see that:
'isvalid : A Boolean value that indicates whether the user's Active Directory account is valid or not valid.'
And please run Get-OwaVirtualDirectory | fl
command in this server, see the value of IsValid parameter and post the result.
Thanks
Sophia Xu
TechNet Community Support
