New Post: Access is denied when Registering a new task - HRESULT: 0x80070005 (E_ACCESSDENIED)

This is your answer, but got lost:

Answering my own question, I was able to finally achieve this using the bare minimum settings.
Moving the Prinicpal properties assignments and placing them instead inside the parameter call of RegisterTaskDefinition and removing the RunLevel parameter did the trick. I was trying to enable the Run with highest Privilege option using a local user account.

Below is the final code for the sake of completeness:

//This task was never installed. So install.
TaskDefinition td = ts.NewTask();
td.RegistrationInfo.Description = "MFT Console Application";

TimeTrigger trigger = new TimeTrigger();
trigger.StartBoundary = DateTime.Now;
trigger.Repetition.Interval = TimeSpan.FromMinutes(30);
td.Triggers.Add(trigger);

td.Actions.Add(new ExecAction(System.Reflection.Assembly.GetExecutingAssembly().Location, null, null));

ts.RootFolder.RegisterTaskDefinition("MFT Console Application", td, TaskCreation.CreateOrUpdate,
   System.Security.Principal.WindowsIdentity.GetCurrent().Name, null, TaskLogonType.S4U);