実行中のタイマーもすべて正常に機能していました。しかし、奇妙な問題に遭遇したとき、cocos2d シーンを再構築する必要がありました。これで、NSTimer を起動できなくなりました。以下の BonusTimetimer は一度も起動されません。
以下はコードです。
BonusTimeTimer = [NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:@selector(CountTimeBonus:) userInfo:nil repeats:YES];
// (lately i added the line below, but it does not help)
[[NSRunLoop mainRunLoop] addTimer:BonusTimeTimer forMode:NSDefaultRunLoopMode];
-(void)CountTimeBonus:(NSTimer *) sender {
    NSLog (@"Method -> Countimebonus");
    if ( (scoreTotal + 37) < TargetScore){
        scoreTotal = scoreTotal + 37;
        TimeBonus = TimeBonus-37;
        NSString *level_timebonus = [NSString stringWithFormat:@"%d", TimeBonus];
        [labelTimeBonus setString: level_timebonus];
        NSString *scorestr = [NSString stringWithFormat:@"%d", scoreTotal];
        [labelMainScore setString: scorestr];
        [[SimpleAudioEngine sharedEngine] playEffect:@"light_switch_.mp3"];
    }
    else {
        // add the Last few points and finish BonusTimer
        scoreTotal = scoreTotal + TimeBonus;
        TimeBonus=0;
        NSString *level_timebonus = [NSString stringWithFormat:@"%d", timebonusgrayed];
        [labelTimeBonus setString: @"" ];
        [labelTimeBonusGrayed setString: level_timebonus];
        NSString *scorestr = [NSString stringWithFormat:@"%d", scoreTotal];
        [labelMainScore setString: scorestr];
        [[SimpleAudioEngine sharedEngine] playEffect:@"light_switch_.mp3"] ;
        [BonusTimeTimer invalidate];
        BonusTimeTimer = nil;
        timeBonusisdone = true;
        timeBonusisactive = false;
    }
}