It could be an indication of a hard disk that's about to fail. Go into My Computer then right click the C:\ drive and go to Properties. From the Tools tab, select Check Now and tick both boxes to find and fix errors automatically. Hit Apply and Ok and you should see a message that tells you it can't do the job now but will do on the next restart. Restart and let it go through that five stage process.
I am yogesh anand, and there is a certain query that on a given system why does a boot volume unmounts so that we get error :-