Anjali - while I don't know much about this, I have come across other posts with the same problem - some have gotten this error after restoring a FT-enabled database from a backup that could've been from when the database was not FT-enabled & some have seen this after applying sp3. Yet others seem to have uninstalled and re-installed it in order to get it to work. See if these links help you any!!!
microsoft link1
microsoft link2
**ASCII stupid question, get a stupid ANSI !!!**