NSMutableArray

Hi,
I used NSMutableArray and added 6 objects to the array,when I run the App on the iphone/simulator the app crashes.
When I delete one object from the array ,the app keep running smoothly.

How can I add more than 5 objects to an NSMutableArray ,or should I use another type of array?

one more question,I defined 3 NSMutableArray ,and defined them in the memmory

Code:

FirstLine = [[NSMutableArray alloc] init];
	 SecondLine = [[NSMutableArray alloc] init];
	 ThirdLine = [[NSMutableArray alloc] init];

the app crashes after I run it,what is the problem?
Thank you.