I retrieve a crash log file, which, after XCode analysis on my archive show the problematic line of code :

Date/Time:       2012-12-08 23:48:08.930 +0100
OS Version:      iPhone OS 5.1.1 (9B206)
Report Version:  104

Exception Type:  EXC_CRASH (SIGABRT)
Exception Codes: 0x00000000, 0x00000000
Crashed Thread:  0

Last Exception Backtrace:
0   CoreFoundation                  0x31a4088f __exceptionPreprocess + 163
1   libobjc.A.dylib                 0x3188b259 objc_exception_throw + 33
2   CoreFoundation                  0x31a40789 +[NSException raise:format:] + 1
3   Foundation                      0x374c73a3 -[NSAssertionHandler     handleFailureInMethod:object:file:lineNumber:description:] + 91
4   Killer                          0x0017ed35 -[CCSprite initWithFile:] (CCSprite.m:201)
5   Killer                          0x0017e419 +[CCSprite spriteWithFile:] (CCSprite.m:93)
6   Killer                          0x00123101 -[Player makeZombie] (Player.m:1363)
7   Killer                          0x00105a51 -[PlayScene endOfKilling:] (PlayScene.m:1438)

Which clearly indicates the second of the two following lines is crashing:

NSLog(@"images %@ %@",self.zombieImage,self.zombieImageDown); 
[self.characterSprite setNormalImage:[CCSprite spriteWithFile:self.zombieImage]];

I know that the crash seem to happend when the user is touching the corresponding CCMeanuItemImage, is there a problem if the user is touching it, while we change the normal et selected images of it ? Is this the right manner to change its image (i do it several times during the game) ?

Thanks for your ideas