there are many many possible reasons. My suggested starting place is with your geometry, though. if you alt J the entire blade assembly into a single piece you only have to animated that piece.
Thanx for the support.
you hit the correct node, problem is in geometry which is now resolved now second prblem still remains i want to show snow fall whcih i can show using particles but the problem is i want snow accumulating on that anemometer please help.