sometimes it may occurs when we forget to add the image view to scrollview. So, make sure that you have added the scrollview to uiview and your image view is added to the scroll view. See the given code it might help you...

Add UIImageView to UIScrollVIew

- (id) init
{
    if(self = [super init])
    {
        scroll = [[UIScrollView alloc] init];
        scroll.scrollEnabled = YES;
        scroll.pagingEnabled = YES;
        scroll.directionalLockEnabled = YES;
        scroll.showsVerticalScrollIndicator = NO;
        scroll.showsHorizontalScrollIndicator = NO;
        scroll.delegate = self;
        scroll.backgroundColor = [UIColor blueColor];
        scroll.autoresizesSubviews = YES;
        scroll.frame = CGRectMake(0, 0, 320, 480);
        [self.view addSubview:scroll];

        view1 = [[UIImageView alloc] init];
        [scroll addSubview:view1];

        view2 = [[UIImageView alloc] init];
        [scroll addSubview:view2];
    }

    return self;
}