The McAfee Security for Microsoft Exchange 8.5.1 On-Demand scan fails to scan any mailboxes on the mailbox server. When debug logging has been enabled, you see the following in the Runscheduledx64.txt file:

Exception in getFolderResults: Microsoft.Exchange.WebServices.Data.ServiceRequestException: The request failed. 

The underlying connection was closed: An unexpected error occurred on a receive.
---> System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a receive.
---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host.
---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host at System.Net.Sockets.Socket.EndReceive(IAsyncResult asyncResult)