Try repair permissions. After every software update, and about every 2 weeks: close all apps and log totally off. Log on, go in Finder, Applications. Utilities, Disk Utility. After the message -getting disk information- select volume (below the hard drive name -upper left corner). Just highlight it. Now look to the lower two things are there near the middle, verify permissions, repair permissions. Click repair permissions If it happens again, Restart in single user terminal (restart and hold Apple S) and there type /sbin/fsck -fy and repeat until the ***file system changed** message stops