The file system structure on the disk is corrupt and unusable
You might see this tricky little bugger in your System Event logs as Event ID 55. Seems simple enough to just run an error check on your system drive to fix the errors (odd in my case as the machine was brand new). Wasn't the first time I've had a bad drive from the start so I proceeded to schedule the diskcheck on the next reboot. File system checked out after finding some issues, but rebooted no problem. Patted myself for a job well done and went to bed.
Then the next morning I get this error in my email (forgot to mention that this Windows 7 Pro machine belongs to one of my managed service clients so I get errors emailed to me when they pop up). Gah! Same thing: The file system structure on the disk is corrupt and unusable. Please run the chkdsk utility on the volume OS.
OK so either the disk is about to die (not really likely as there are no issues popping up with the system other than this alert). A quick Google search on an obscure site (the particular forum post eludes me at the moment) mentions that possibly a Windows recovery point is corrupted. Easy enough to test. Run a disk cleanup on the drive. After it finds items, go to the Options tab and click the Clean Up button for System Restore and Shadow Copies.