crash while removing objects from NSMutableArray

Question

In my iphone project (ARC enabled) i have a nsmuatble array which contains some 5 managed objects (which are retrieved from core data ) and in some scenario i n

Answer 1

From the exception it's very evident that at some point you are assigning an immutable instance to your mutable array. From the comments I could make out that you were sorting surveys and sorted array was returning immutable array. Type casting will not do good for getting mutableCopy of an immutable object.

NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor1,nil]; 
surveys = (NSMutableArray *) [[[NSMutableArray alloc]initWithArray:surveys ] sortedArrayUsingDescriptors:sortDescriptors];

Instead of it use

[surveys sortUsingDescriptors: @[sortDescriptor1]];