PHImageManager is not working iphone4s

[smilydronavalli]

HI,

    for (PHAsset *asset in photoAssets) {
        CGSize targetSize = CGSizeMake((CGRectGetWidth(_mycollection.bounds) - 20*2) * [UIScreen mainScreen].scale, (CGRectGetHeight(_mycollection.bounds) - 20*2) * [UIScreen mainScreen].scale);
        [imageManager requestImageForAsset:asset targetSize:PHImageManagerMaximumSize contentMode:PHImageContentModeAspectFill options:options resultHandler:^(UIImage *image, NSDictionary *info) {
            [mutableImages addObject:image];
        }];
    } 

Th above method is not working in iphone4.suddenly it's not working.Please kindly suggest me how to resolve this issue and it is important for me.

Thanks inadvance