I returned off of vacation to find that my scheduled task for defragging my hard drive was failing on my machine. Come to find out, the defragging process had not been started for over three weeks. Scratching my head, I went to investigate why. Well, right before I went on vacation, I was prompted to change my Windows password (The company I work for has a 90-day change password policy). So, I changed it and thought nothing of it. As you know, in order to run a successful scheduled task for defragging, you must provide a username and password. If you change your Windows password, you must change your password for your defrag scheduled task as well. If you don't, your "Last Run Result" will display a FAIL!!!
Lesson learned: If you have a company password change policy, ensure you update you defrag password as well.