I've had an oddity occur ( at least for me). Two system folders on two separate drives have lost there virtue. Both in suceession have lost their blessedness. Two suspected causes. Installation of a superdrive which went flawlessly as far as I could tell, and both disks were checked by DiskWarrior X 3.0 prior to discovery. Likely cause anyone? Both disks have had system clean install and are solid at present. Dare I run DW for laughs?