Hi @Venkatesh_venkatesh ,
comand for the restart is "nlserver restart service_name@istance_name" .
In your case it should be "nlserver restart mta@wvneoweb003-c" or "nlserver restart mta@default" .
Provided error means that you tried to stop proccees which is not working (assuming that you instance name is correct). Before restart you can use "nlserver pdump" to see the list of active services or "nlserver monitor -missing" to see not started services.
Of course, first check if mta service is on you application server or it is on separate server.
Regards,
Milan