App crashes in 5.1 simulator, runs fine in 5.0

My app crashes on the xcode iOS simulator 5.1, but runs fine on 5.0

This is the message I get in xcode, does it mean something to you?

*** Terminating app due to uncaught exception 'NSRangeException', reason: '-[__NSCFConstantString characterAtIndex:]: Range or index out of bounds'
*** First throw call stack:
(0x29c1022 0x20abcd6 0x2969a48 0x29699b9 0x298df4d 0x156e8a 0xf3909 0xf2c99 0x51602 0x8b77b 0x2ce90 0x2c2f9 0x2ba15 0x2d8cd 0x8d380 0x10e0f0 0xce89 0xbab6 0x3afe 0xbc5eb6 0x2995936 0x29953d7 0x28f8790 0x28f7d84 0x28f7c9b 0x244e7d8 0x244e88a 0xee7626 0x2226 0x2195 0x1)
terminate called throwing an exception(lldb)

Can you send me your app, and explain to me in details how to get the crash?

Thanks

I've sent you a PM, thanks!

New input on this problem:

I've finally identified the exact thing that makes the app crash, though I don't understand why it would do that.

When you click on the button "New Game", it saves a bunch of values to the INI file.
There are 2 specific values that make the app crash. If I remove them and leave everything else, the crash does not occur.
They were the last 2 values created in the INI file, though I don't know if this has any kind of importance.
Among many things, I tried to change the name of the group in which they are saved. The values were saved in the group "Gameplay", I switched them to the group "Poney" (or anything else), and the app did run fine. The odd thing is that I have other values written in the group "Gameplay" and that does not seem to be a problem for them.

I really have no idea as why writing those values in this group results in a crash, and only in 5.1 simulator, but I hope someone will understand this mystery. :)