cvCaptureFromCam is working but cvQueryFrame returns NULL

I have seen most people have problems with cvCaptureFromCam where as for me cvCaptureFromCam(-1) is working fine and returning a non-null pointer; however cvQueryFrame is returning NULL. To go in details I used cvGrabFr开发者_JAVA技巧ame and cvRetrieveFrame. cvGrabFrame is returning 1 that means its successfully grabbed the frame but cvRetrieveFrame returned NULL. Can somebody please guide me.