Error: 'Attempted to perform another operation with a fetch already in progress', Only in iOS 6 - objective-c

Question

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Attempted to perform another operation with a fetch already in progress'
First time my application working fine..but then after every time my app is crashed due to the above error and its only happened in iOS6 version devices. but my app is working fine in iOS7 or upper version devices.
The below is stack trace:
(
0 CoreFoundation 0x32e5b2bb <redacted> + 186
1 libobjc.A.dylib 0x3aadb97f objc_exception_throw + 30
2 CoreData 0x32bf5207 <redacted> + 94
3 CoreData 0x32bf591d <redacted> + 92
4 CoreData 0x32c06387 <redacted> + 58
5 CoreData 0x32c04d19 <redacted> + 624
6 CoreData 0x32bfe089 <redacted> + 312
7 CoreData 0x32bfd73f <redacted> + 682
8 CoreData 0x32bfd205 <redacted> + 468
9 CoreData 0x32bfc61d <redacted> + 1644
10 CoreData 0x32bfaf17 <redacted> + 646
11 WhatDidIWear 0x000b1875 -[WDIWDatabase(Years) years] + 848
12 WhatDidIWear 0x000a9b2d -[WDIWCalendar years] + 56
13 WhatDidIWear 0x00095c8f -[YearsViewController initWithNibName:bundle:] + 382
14 WhatDidIWear 0x000945bb -[TemplateViewController initWithDefaultNibName] + 62
15 WhatDidIWear 0x00093567 -[TabBarController yearsVC] + 134
16 WhatDidIWear 0x00093713 -[TabBarController homeViewControllers] + 46
17 WhatDidIWear 0x0008f49b -[TabBarController viewDidLoad] + 510
18 UIKit 0x34cf82d5 <redacted> + 228
19 WhatDidIWear 0x0008e927 -[AppDelegate tabBarController] + 134
20 WhatDidIWear 0x0008de65 -[AppDelegate application:didFinishLaunchingWithOptions:] + 980
21 UIKit 0x34cc3ad9 <redacted> + 252
22 UIKit 0x34cc3663 <redacted> + 1190
23 UIKit 0x34cbb84b <redacted> + 698
24 UIKit 0x34c63c39 <redacted> + 1004
25 UIKit 0x34c636cd <redacted> + 72
26 UIKit 0x34c6311b <redacted> + 6154
27 GraphicsServices 0x369555a3 <redacted> + 590
28 GraphicsServices 0x369551d3 <redacted> + 34
29 CoreFoundation 0x32e30173 <redacted> + 34
30 CoreFoundation 0x32e30117 <redacted> + 138
31 CoreFoundation 0x32e2ef99 <redacted> + 1384
32 CoreFoundation 0x32da1ebd CFRunLoopRunSpecific + 356
33 CoreFoundation 0x32da1d49 CFRunLoopRunInMode + 104
34 UIKit 0x34cba485 <redacted> + 668
35 UIKit 0x34cb7301 UIApplicationMain + 1120
36 WhatDidIWear 0x0008d97f main + 230
37 libdyld.dylib 0x3af12b20 <redacted> + 0
)
I am frustrated now for not solving the above error.
Please give me an idea to solve the above stuff.