My end users can not run disk defrag in windows 7 if they are anything except admins (which we do not want to allow for obvious reasons).
When users have anything but admin rights the defrag will not run. I went in and set the permission for "Users" and "Everyone" to Full control and this does not work either. I also went into properties for the Defrag and hit the compatibility tab to set the "Run this program as an administrator" to active and everything is greyed out. I even tried this on a system that was never on our network and took our group policy.