développement iPhone: pointeur être libérés n'a pas été alloué

j'ai eu ce message à partir du débogueur:

Pixture(1257,0xa0610500) malloc: *** error for object 0x21a8000: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug

j'ai donc fait un peu de traçage et a obtenu:

(gdb) shell malloc_history 1257 0x21a8000

ALLOC 0x2196a00-0x21a89ff [size=73728]: thread_a0610500 |start | main | UIApplicationMain | GSEventRun | GSEventRunModal | CFRunLoopRunInMode | CFRunLoopRunSpecific | __CFRunLoopDoObservers | CA::Transaction::observer_callback(__CFRunLoopObserver*, unsigned long, void*) | CA::Transaction::commit() | CA::Context::commit_transaction(CA::Transaction*) | CALayerDisplayIfNeeded | -[CALayer _display] | CABackingStoreUpdate | backing_callback(CGContext*, void*) | -[CALayer drawInContext:] | -[UIView(CALayerDelegate) drawLayer:inContext:] | -[AvatarView drawRect:] | -[AvatarView overlayPNG:] | +[UIImageUtility createMaskOf:] | UIGraphicsGetImageFromCurrentImageContext | CGBitmapContextCreateImage | create_bitmap_data_provider | malloc | malloc_zone_malloc

et je ne comprends vraiment pas ce que je fais de mal. voici le code de la [UIImageUtility createMaskOf:] fonction:

+ (UIImage *)createMaskOf:(UIImage *)source {
    CGRect rect = CGRectMake(0, 0, source.size.width, source.size.height);
    UIGraphicsBeginImageContext(CGSizeMake(source.size.width, source.size.height));
    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextTranslateCTM(context, 0, source.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    UIImage *original = [self createGrayCopy:source];

    CGContextRef context2 = CGBitmapContextCreate(NULL, source.size.width, source.size.height, 8, 4 * source.size.width, 
                                                   CGColorSpaceCreateDeviceRGB(), kCGImageAlphaNoneSkipLast);
    CGContextDrawImage(context2, CGRectMake(0, 0, source.size.width, source.size.height), original.CGImage);
    CGImageRef unmasked = CGBitmapContextCreateImage(context2);

    const float myMaskingColorsFrameColor[6] = { 1,256,1,256,1,256 };
    CGImageRef mask = CGImageCreateWithMaskingColors(unmasked, myMaskingColorsFrameColor);

    CGContextSetRGBFillColor (context, 256,256,256, 1);
    CGContextFillRect(context, rect);
    CGContextDrawImage(context, rect, mask);

    UIImage *whiteMasked = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return whiteMasked;
}

l'autre fonction personnalisée appelée avant que est la suivante:

- (UIImage *)overlayPNG:(SinglePart *)sp {
NSLog([sp description]);
//Rect and context setup
CGRect rect = CGRectMake(0, 0, sp.image.size.width, sp.image.size.height);
NSLog(@"%f x %f", sp.image.size.width, sp.image.size.height);
//Create an image of a color filled rectangle
UIImage *baseColor = nil;
if (sp.hasOwnColor) {
baseColor = [UIImageUtility imageWithRect:rect ofColor:sp.color];
} else {
SinglePart *facePart = [editingAvatar.face.partList objectAtIndex:0];
baseColor = [UIImageUtility imageWithRect:rect ofColor:facePart.color];
}
//Crete the mask of the layer
UIImage *mask = [UIImageUtility createMaskOf:sp.image];
mask = [UIImageUtility createGrayCopy:mask];
//Create a new context for merging the overlay and a mask of the layer
UIGraphicsBeginImageContext(CGSizeMake(sp.image.size.width, sp.image.size.height));
CGContextRef context2 = UIGraphicsGetCurrentContext(); 
//Adjust the coordinate system so that the origin 
//is in the lower left corner of the view and the 
//y axis points up 
CGContextTranslateCTM(context2, 0, sp.image.size.height); 
CGContextScaleCTM(context2, 1.0, -1.0); 
//Create masked overlay color layer
CGImageRef MaskedImage = CGImageCreateWithMask (baseColor.CGImage, mask.CGImage);
//Draw the base color layer
CGContextDrawImage(context2, rect, MaskedImage);
//Get the result of the masking
UIImage* overlayMasked = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
UIGraphicsBeginImageContext(CGSizeMake(sp.image.size.width, sp.image.size.height));
CGContextRef context = UIGraphicsGetCurrentContext();
//Adjust the coordinate system so that the origin 
//is in the lower left corner of the view and the 
//y axis points up 
CGContextTranslateCTM(context, 0, sp.image.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
//Get the result of the blending of the masked overlay and the base image
CGContextDrawImage(context, rect, overlayMasked.CGImage);
//Set the blend mode for the next drawn image
CGContextSetBlendMode(context, kCGBlendModeOverlay);
//Component image drawn
CGContextDrawImage(context, rect, sp.image.CGImage);
UIImage* blendedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
CGImageRelease(MaskedImage);
return blendedImage;
}