error in quiting powerpoint app

hi , I am using powerpoint object libraray for office xp ,in my app when ever i try to close powerpoint app ,either with a presenation opened or closed just before .The powerpoint application gives an error,but if i donot open any application then it goes fine .I am using powerpointobj.quite() for this .Please .... let me know......Waiting for reply's. thanx in advance...