Returns null.
The AsyncResult.SyncProcessMessage(IMessage) method implements the System.Runtime.Remoting.Messaging.IMessageSink interface. You do not need to call this method directly. It is intended for use by the remoting infrastructure of the .NET Framework.
AsyncResult.SyncProcessMessage(IMessage) invokes the consumer code's AsyncCallback delegate. It also sets the System.Runtime.Remoting.Messaging.IMethodReturnMessage instance returned by the AsyncResult.GetReplyMessage method. If the msg parameter is of type System.Runtime.Remoting.Messaging.IMethodReturnMessage, the same object is returned by AsyncResult.GetReplyMessage. Otherwise, a reply message that contains a remoting exception is returned.
AsyncResult.SyncProcessMessage(IMessage) also modifies the value returned by the AsyncResult.IsCompleted property.