Disable ECP from Internet facing Issue

Hi,

I plan to disable ECP from Internet access. I try to use Set-ECPVirtualDirectory -Identity "CAS01\ecp (default web site)" -AdminEnabled $false it give error

The version of Internet Information Services (IIS) that is running on server 'CAS01.masb.com' can't be determined.
This error can occur due to network connectivity issues. Check the availability of your network and try again.
Parameter name: Server
    + CategoryInfo          : InvalidArgument: (CAS01\ecp (Default Web Site):ADObjectId) [Set-EcpVirtualDirectory], Ar
   gumentException
    + FullyQualifiedErrorId : [Server=MAILBOX02,RequestId=42d5f0b8-9e83-49d7-a308-68f87ac7e643,TimeStamp=12/3/2015 10:
   42:53 PM] [FailureCategory=Cmdlet-ArgumentException] 5636C4E3,Microsoft.Exchange.Management.SystemConfigurationTas
  ks.SetEcpVirtualDirectory
    + PSComputerName        : cas01.masb.com

We mange to set it on CAS02.

May I know how to solve this issue on CAS01. We already set CAS03 for internal use only

Thank you

Best regards,

See Keong