Well this is a simple issue, need not panic. If refreshing the project, rebuilding it or cleaning did not work. Then probably u might have added an additional library which is not necessary.
solution : Go to Project » Properties » Java Build Path » Libraries and remove all except the "Android X.Y" (in my case Android 1.5). click OK. Go to Project » Clean » Clean projects selected below » select your project and click OK. That should work.