Thanks for the quick reply. To clarify - most of these are different Annual Tasks (eg Birthdays) with end times 'Forever'. Now you point it out, it is obvious that a "Forever" Task can never be 'Complete'. The problem is that in the Manager window the past (2012)occurrences of these Task are still shown as 'Needs Action' even though I have tried to 'Complete' this years occurrence.
For Birthdays I would reccomend using events instead of tasks. Works the same, but... I never heard of a "Needing Action Birthday"
That's right, the Manager never will show the task as completed because it could never be completed. Think the Manager as the window to lookout all the events/tasks. In this case, is one task only but with many instances. In the manager you can't see all the instances but the original one.