Frozen Start Button

My problem is I have a couple of users that have their start button frozen. It gets stuck in the depressed position. It is not even right clickable. Everything else works fine for the users. This happened to me once before about 6 months ago with a few users. At that time the problem occured when I was creating an OU structure and had moved useres to their respective OU’s. I was unable to correct it and my only solution was to create new user accounts for each user that had the problem. I haveseen this question asked a few times but have not seen any solutions. This problem happens regardless of the workstation the user logs into