I am sure you have googled this and there are several probable causes. An incomplete installation, an incomplete uninstall, improper deletion of applications or hardware. It can also be caused if your computer is recovered from a virus or adware/spyware attack or by an improper shutdown of the computer.
Can you get into safe mode? Do you by any chance have AVG installed? (I had this error on a clients netbook last week and it was a residual AVG file that caused the problem.)