service contract attribute is not inherited, so if the interface or class you are using to define your Service contract inherits from another Service contract, you must explicitly use the ServiceContract-Attribute to declare the subtype as a Service contract as well.
Syntax to declare Service Contract
' VB
_
Public Interface ITaskManagerService
' Etc...
End Interface
// C#
[ServiceContract(Name = "TaskManagerService",
Namespace = "http://schemas.fabrikam.com/2008/04/tasks/")]
public interface ITaskManagerService
{
// Etc...
}