To throw more wood on this fire...... Consider that you cannot change your motor oil filter while the motor is running without spilling something. This is the same procedure that people attempt when trying to repair permissions with Disk Utility while booted to the internal hard drive. It is ill-advised to do this. In order to make a change on the hard drive, it has to be the target of the action. If it is constantly moving, you do not have a clear target and may miss your point of aim. If it is the boot drive, it is in constant motion and liable to cause a problem. If you boot to a CD or external hard drive, the internal drive is in a state of rest and isn't moving as radically as it would if it were the boot drive. The files on the drive will be receptive to an action from outside and there is less likelihood of error. I always try to use the latest OS version CD that I can get my hands on to make repairs with. That's all, folks.