Did you ever get this error on a Joomla 1.7 or 2.5 site? If yes, you probably searched the net and was dazzled by the amount of hits. Today I got this:
About 33,900 results (0.28 seconds)
But nobody seems to know what exactly happens when you got this error. Might be a halfway uninstalled/damaged component (less likely, most of the cases), might be other similar causes. But the cause may be very simple - you might be run out from your server space!!
So, go to the hosting panel, and check your disk usage stats! And delete things you might not need - as content of /temp and /cache. And check your site!
Chances are, that you just get rid of this mysterious error. If not, you can check still the other 33k+ tips!