Cannot Edit Tasks in List View

Hi there -

I can no longer edit my tasks while looking at them in a list view.

In other words, if I have my tasks arranged in a list, I can no longer check
the "Complete" checkbox to mark the task as complete. I can no longer change
the due date from 5/26/2007 to 5/28/2007. I cannot change the priority of a
task, etc.

With my tasks in list view, the ONLY thing I can do is to select the task,
then open the task, and then change the attributes of the task.

I use Outlook 2003 SP2 on a Vista machine. Outlook had been operating
properly on this machine for several months.

Thanks for any input.