Error calling on managedobject with EXC_BAD_ACCESS - iphone

Question

I searched a lot for this error and was not able to find a solution.
I have my managedObject:
lazy var managedObjectContext: NSManagedObjectContext = {
let coordinator = self.persistentStoreCoordinator
var managedObjectContext = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
managedObjectContext.persistentStoreCoordinator = coordinator
return managedObjectContext
}()
and I have a Singleton class
lazy var managedObjectContext : NSManagedObjectContext? = {
if let appDelegate = UIApplication.sharedApplication().delegate as? AppDelegate {
return appDelegate.managedObjectContext
}
return nil
}()
I have a method which is called lot of time whenever I update / delete / load data from database
class func LoadDatabase(tableName: String, predicateString: String, predicateIntValue: Int) -> [AnyObject]? {
do {
let managedObjectContext = Singleton.sharedInstance.managedObjectContext
if managedObjectContext == nil {
return nil
}
let fReq: NSFetchRequest = NSFetchRequest(entityName: tableName)
if predicateString != "" {
fReq.predicate = NSPredicate(format: predicateString, predicateIntValue)
}
var result: [AnyObject]
do {
if managedObjectContext == nil {
return nil
}
result = try managedObjectContext!.executeFetchRequest(fReq)
} catch {
return nil
}
// update exist event
if
result.count != 0 {
return result
}
} catch let error1 as NSError {
print("No values to load for table: \(error1)")
}
return nil
}
I think I have problem on concurrence access. When the app starts it stars asynchronous requests to update the database. But I also call the method LoadDatabase from varius controller. Once the asynchronous call done with updating the datable, it call another method to delete datas which are not more in remote database.
This is what I get. This does not happens always.
I tried to change to MainQueueConcurrency but now I am getting also this error:
2016-03-20 21:27:01.371 Tamil League[1070:245784] CoreData: error: Serious application error. Exception was caught during Core Data change processing. This is usually a bug within an observer of NSManagedObjectContextObjectsDidChangeNotification. -[__NSCFSet addObject:]: attempt to insert nil with userInfo (null)
2016-03-20 21:27:01.371 Tamil League[1070:245784] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFSet addObject:]: attempt to insert nil'
*** First throw call stack:
(0x24a9e2eb 0x2426adff 0x24a9e231 0x249e7fe5 0x261eb683 0x261ea063 0x261e2dfb 0x24a60b21 0x24a5ee17 0x24a5f255 0x249b1bb9 0x249b19ad 0x25c2baf9 0x28c9dfb5 0xa6d5c 0x24664873)
libc++abi.dylib: terminating with uncaught exception of type NSException
Does anyone know how to solve this?