Probably a "housekeeping" issue, that is, you may need to do some system maintenance chores like repairing permissions, starting up in Single User mode, etc. If you sleep your system and don't restart every so often, this kind of thing can happen.
I'd go with Repair Permissions, then restart the system. That could be followed by running Disk Warrior on all disks and Single User mode if it persists. Re-install OS X as a last resort.