App crashes very rare on start up

I have a strange problem with my app, sometimes, very rare in fact, when run on iPhone4, it crashes right at the beginning, I got the crash log, but I really can't make anything of it. I'm kind of stuck, where should I look? Here is the log:

0   libsystem_kernel.dylib          0x34c96a1c __pthread_kill + 8
1   libsystem_c.dylib               0x328ee3b4 pthread_kill + 52
2   libsystem_c.dylib               0x328e6bf8 abort + 72
3   libsystem_c.dylib               0x329146d4 __assert_rtn + 140
4   My App                  0x0000fb8c 0x1000 + 60300
5   My App                  0x0000fec4 0x1000 + 61124
6   My App                  0x00009ffc 0x1000 + 36860
7   CoreFoundation                  0x359c979c __invoking___ + 60
8   CoreFoundation                  0x35941436 -[NSInvocation invoke] + 102
9   My App                  0x0005f408 0x1000 + 386056
10  My App                  0x0005c9b8 0x1000 + 375224
11  CoreFoundation                  0x3593656a -[NSObject(NSObject) performSelector:withObject:withObject:] + 18
12  My App                  0x000b60d4 0x1000 + 741588
13  My App                  0x000b6bc0 0x1000 + 744384
14  My App                  0x000b8c9c 0x1000 + 752796
15  UIKit                           0x35584bee -[UIWindow _sendTouchesForEvent:] + 362
16  UIKit                           0x35584568 -[UIWindow sendEvent:] + 256
17  UIKit                           0x3556d30c -[UIApplication sendEvent:] + 292
18  UIKit                           0x3556cc4c _UIApplicationHandleEvent + 5084
19  GraphicsServices                0x35350e70 PurpleEventCallback + 660
20  CoreFoundation                  0x3599da90 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 20
21  CoreFoundation                  0x3599f838 __CFRunLoopDoSource1 + 160
22  CoreFoundation                  0x359a0606 __CFRunLoopRun + 514
23  CoreFoundation                  0x35930ebc CFRunLoopRunSpecific + 224
24  CoreFoundation                  0x35930dc4 CFRunLoopRunInMode + 52
25  GraphicsServices                0x35350418 GSEventRunModal + 108
26  GraphicsServices                0x353504c4 GSEventRun + 56
27  UIKit                           0x35597d62 -[UIApplication _run] + 398
28  UIKit                           0x35595800 UIApplicationMain + 664
29  My App                  0x00002118 0x1000 + 4376
30  My App                  0x00002084 0x1000 + 4228

I was not able to find any pattern for the crash, it simply happens like maybe once in 30-40 app start-ups. What beats me, beside the fact that I don't know how the interpret the crash log, is why this happens so rare, with no apparent reason?

You need to symbolicate that crash log before you can see exactly which part of your code is crashing.