can not run on iphone simulater

[yangshengchaoios]

[yangshengchaoios]

The program will crash at the following lines: so, why?

    // @HACK: Come up with a better pattern for removing observers.
    @try {
        [tweenOperation removeObserver:[PRTween sharedInstance] forKeyPath:@"period.tweenedValue"];
    } @catch (id exception) {
    }
    @try {
        [tweenOperation removeObserver:[PRTween sharedInstance] forKeyPath:@"period.tweenedLerp"];
    } @catch (id exception) {
    }