New Post: Two Bugs...

Dim taskServiceObject As New TaskScheduler.TaskService()
Dim taskObject As TaskScheduler.Task = taskServiceObject.GetTask("my task")

If taskObject IsNot Nothing Then
  If taskObject.Definition.Settings.MultipleInstances <> TaskScheduler.TaskInstancesPolicy.Parallel Then
    task.Definition.Settings.MultipleInstances = TaskScheduler.TaskInstancesPolicy.Parallel
    task.RegisterChanges()
    task.Dispose()
  End If
End If

taskServiceObject.Dispose()