Try putting the image into a button first:
UIImage *theImage = [UIImage imageNamed:@"image.png"];
UIButton *theButton = [UIButton buttonWithType:UIButtonTypeCustom];
theButton.bounds = CGRectMake(0, 0, theImage.size.width, theImage.size.height);
[theButton setImage:theImage forState:UIControlStateNormal];
UIBarButtonItem *theBarButtonItem = [[UIBarButtonItem alloc] initWithCustomView:theButton];
[theButton addTarget:self action:@selector(MenuSlider:) forControlEvent:UIControlEventTouchUpInside];
self.navigationItem.leftBarButtonItem = barItem;