NSFetchedResultsController issue on iOS4 - ios

Question

I am developing an application which uses CoreData. The view contains a UITableView (containing around 50 elements) which uses a NSFetchedResultsController. There is also a "Pull to refresh" which permits to refresh the stored data after a WS call (in another thread with a new managed object context).
Everything is working fine on iOS5: the database and the tableview are refreshed when I perform a "Pull to refresh". However there is a problem with iOS4. The first "performFetch" works when the application is launched (the tableview contains all database records) but I've got the following error when I perform a "Pull to refresh":
2012-02-29 11:56:09.119 Nanopost[1996:207] *** Terminating app due to uncaught exception 'NSObjectInaccessibleException', reason: 'CoreData could not fulfill a fault for '0x5c3c760 <x-coredata://E176B0A1-275B-4332-9231-49FD88238C2B/Ads/p231>''
*** Call stack at first throw:
(
0 CoreFoundation 0x02bfe919 __exceptionPreprocess + 185
1 libobjc.A.dylib 0x02e595de objc_exception_throw + 47
2 CoreData 0x028b833f _PFFaultHandlerLookupRow + 1407
3 CoreData 0x028b5ee3 _PF_FulfillDeferredFault + 499
4 CoreData 0x028b9f3f _sharedIMPL_pvfk_core + 95
5 CoreData 0x0292a010 _PF_Handler_Public_GetProperty + 160
6 Foundation 0x02442c4f -[NSSortDescriptor compareObject:toObject:] + 128
7 CoreData 0x0297db5e +[NSFetchedResultsController(PrivateMethods) _insertIndexForObject:inArray:lowIdx:highIdx:sortDescriptors:] + 286
8 CoreData 0x0297e1b2 -[NSFetchedResultsController(PrivateMethods) _postprocessInsertedObjects:] + 402
9 CoreData 0x029841bc -[NSFetchedResultsController(PrivateMethods) _managedObjectContextDidChange:] + 1804
10 Foundation 0x02380c1d _nsnote_callback + 145
11 CoreFoundation 0x02bd6cf9 __CFXNotificationPost_old + 745
12 CoreFoundation 0x02b5611a _CFXNotificationPostNotification + 186
13 Foundation 0x023767c2 -[NSNotificationCenter postNotificationName:object:userInfo:] + 134
14 CoreData 0x028c0519 -[NSManagedObjectContext(_NSInternalNotificationHandling) _postObjectsDidChangeNotificationWithUserInfo:] + 89
15 CoreData 0x028f802b -[NSManagedObjectContext mergeChangesFromContextDidSaveNotification:] + 1579
16 Foundation 0x02395e9a __NSThreadPerformPerform + 251
17 CoreFoundation 0x02bdfd7f __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 15
18 CoreFoundation 0x02b3e2cb __CFRunLoopDoSources0 + 571
19 CoreFoundation 0x02b3d7c6 __CFRunLoopRun + 470
20 CoreFoundation 0x02b3d280 CFRunLoopRunSpecific + 208
21 CoreFoundation 0x02b3d1a1 CFRunLoopRunInMode + 97
22 GraphicsServices 0x031e62c8 GSEventRunModal + 217
23 GraphicsServices 0x031e638d GSEventRun + 115
24 UIKit 0x0063cb58 UIApplicationMain + 1160
25 Nanopost 0x0000230a main + 170
26 Nanopost 0x00002255 start + 53
)
terminate called after throwing an instance of '_NSCoreDataException'
When I initialize the "NSFetchRequest", I set the "FetchBatchSize" to 20 (randomly):
[l_FetchRequest setFetchBatchSize:20];
But if I set the "FetchBatchSize" to 25:
[l_FetchRequest setFetchBatchSize:25];
... No more crashes on iOS4 and I don't know why and I want to understand this issue :) I don't think that this line is the real problem. Maybe it indicates another problem somewhere?
Thank you very much in advance for your answers!
Thomas

Answer 1

Is there a reason you are using a different context? I don't switch mine, and I have a pretty similar sounding app.
One thing you might compare to is this very handy CoreDataTableViewController:
http://www.stanford.edu/class/cs193p/cgi-bin/drupal/node/289
I use it and haven't had any issues (though I am not running in iOS 4). You might compare how you hooked up the fetchedResultsController.
One other point - do you have the catch-all breakpoint to push the debugger as soon as an exception is raised? If not, add it (breakpoints, + to add, "Add Exception Breakpoint" and keep defaults). That will put you into the debugger right on the line that raises the exception, which should be useful.
Good luck,
Damien