Closed Unassigned: NullReferenceException when display Run Times in TaskEditDialog [12302]

When I try displaying the schedule for the an __existing__ task, I see the following error in the Run Times tab.

Unable to show the run times for this task.
Error: System.NullReferenceException: Object references not set to an instance of an object.
at Microsoft.Win32.TaskScheduler.TaskService.NewTask()
at Microsoft.Win32.TaskScheduler.TaskPropertiesControl.runTimesTab_Enter(Object sender, EventArgs e)

If I click ok, Windows display a Quit, Continue, Ignore dialog box and nothing gets saved.

Note that is only happening when I try to modify an existing task. If I create a new task, the RunTimes tab gets filled correctly.