If you have installed Exchange 2013 on your servers then you need to manage it with the new ECP, this is accessed via the below.
Cannot Access ECP – OWA Loads Instead
If you see that OWA opens instead of the ECP then this is because you are trying to access the ECP from a CAS server, the ECP console must be ran from a server that has the Mailbox role installed. Another symptom of this is when you try and run the Exchange 2013 Toolbox.
Cannot Access Exchange 2013 Toolbox
Again if you do not have the Exchange 2013 Mailbox role on the server you try to run the Exchange 2013 Toolbox on then you will see the error below.
Exception type: System.Runtime.Serialization.SerializationException
Exception stack trace:
at Microsoft.ManagementConsole.Internal.IMessageClient.ProcessRequest(Request request)
at Microsoft.ManagementConsole.Executive.RequestStatus.BeginRequest(IMessageClient messageClient, RequestInfo requestInfo)
at Microsoft.ManagementConsole.Executive.Operation.OnThreadTransfer(SimpleOperationCallback callback)