Duplicate existing Task using RegisterTaskDefinition fail

[eng-marani]

I would like to create a duplicated task from an existing task, in disabled state, preserving credentials.
Of course, I'm running under admin.

This is my actual code, but RegisterTaskDefinition() does not complete the job raising an exception "Invalid credentials"

        Public Function DuplicateTask(byval _OldTask as Task, byval NewTaskName As String) As Task
            Using ts As New TaskService()
                Dim td As TaskDefinition = _OldTask.Definition
                Dim t As Task = RuleDesignerFolder.RegisterTaskDefinition(NewTaskName, td)
                Return t
            End Using
        End Function

What I'm doing wrong ?

[eng-marani]

Using this overload effectively, I do not have any crash, i wonder anyway why i can't use the previous one, expecting also the principal and security to be copied from the definition

Dim t As Task = RuleDesignerFolder.RegisterTaskDefinition(NewTaskName, td, TaskCreation.Create, td.Principal.UserId)