Exception SIGABRT in dispatch_async _block_invoke for NSMutableDictionary setObject - iphone

Question

I observed no crash in my simulator runs but it is consistently happening on my iPhone (iOS 5.1) and iPad (iOS 6.1).
After much effort I symbolicated the crash to point the erroneous line in my code - here this symbolicated log goes:
Exception Type: EXC_CRASH (SIGABRT)
Exception Codes: 0x0000000000000000, 0x0000000000000000
Crashed Thread: 12
Last Exception Backtrace:
0 CoreFoundation 0x342fd29e 0x3423b000 + 795294
1 libobjc.A.dylib 0x3c17197a 0x3c169000 + 35194
2 CoreFoundation 0x342fd1c0 0x3423b000 + 795072
3 CoreFoundation 0x3425e864 0x3423b000 + 145508
4 MyApp 0x0011626c __55-[MSCollectionViewController updateUI:]_block_invoke (MSCollectionViewController.m:385)
5 libdispatch.dylib 0x3c58911a 0x3c587000 + 8474
6 libdispatch.dylib 0x3c58d95c 0x3c587000 + 26972
7 libdispatch.dylib 0x3c58dabc 0x3c587000 + 27324
8 libsystem_c.dylib 0x3c5bda0c 0x3c5b7000 + 27148
9 libsystem_c.dylib 0x3c5bd8a0 0x3c5b7000 + 26784
As anyone can guess, the error is on Line#385 of my MSCollectionViewController.m file. However I am still unable to see what could cause such a crash, as it runs fine on simulator.
UPDATED CODE:
Note that now it is crashing at [m_photoArray addObject:photoDetailDict];
I added m_photoArray (NSMutableArray) initialization for reference which I am doing on main thread.
Here is my code, including the problematic line # 385 as comment:
__block NSString * flickrPhotoArrayPath = [Commons getFlickrJSONPathForMuseumURI:argURI];
if (m_photoArray)
{
[m_photoArray removeAllObjects];
}
else
{
m_photoArray = [[NSMutableArray alloc] init];
}
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0),
^{
NSArray *arrayFromFlickrJSON = [NSArray arrayWithContentsOfFile:flickrPhotoArrayPath];
if (!arrayFromFlickrJSON || [arrayFromFlickrJSON count]==0)
return;
if (bViewVisible)
{
[SVProgressHUD showWithStatus:#"Fetching Photos" maskType:SVProgressHUDMaskTypeBlack];
}
for (id photo in arrayFromFlickrJSON)
{
NSDictionary * dict = (NSDictionary *)photo;
NSMutableDictionary * photoDetailDict = [dict mutableCopy];
NSString * filePath = [photoDetailDict objectForKey:#"photoFilePath"];
UIImage *image = [UIImage imageWithContentsOfFile:filePath];
[photoDetailDict setObject:image forKey:#"photoImage"];
//AND HERE GOES THE CRASH!!!
[m_photoArray addObject:photoDetailDict]; //Line 385
}
dispatch_async(dispatch_get_main_queue(), ^{
if ([SVProgressHUD isActive])
[SVProgressHUD dismiss];
//More code to update UI
});
});
Here goes my 2 questions:
What is it in NSMutableDictionary setObject that I am seeing this crash?
Why don't I observe it with same set of data on my simulator?
UPDATE:
Instantly found glitch in my code:
The issue maybe in [photo mutableCopy]; - photo is of id type, not NSDictionary. I need to cast it to NSDictionary first before performing mutableCopy.
The major question still remains is - why simulator allows it?
Heck, why even compiler allows it?