So, here's how it goes.

I am currently working on Cocos2d game, which consists of many Obstacles. One obstacle gets added on the screen at an interval of 10 seconds like this.

ObstacleSprite* newObstacle = [ObstacleSprite spriteWithFile:@"Obstacle.png" rect:CGRectMake(0, 0, 20, 20)];
newObstacle.position = ccp(mainPlayer1.position.x,10);
[self addChild:newObstacle];

[self.arrayForObstacles addObject:newObstacle];

Now, I insert these obstacles into the arrayForObstacles because I also want to keep checking whether the Obstacles and MainPlayer don't collide.

I check it with the help of this function.

- (void) checkCollisionWithObstacle
{
    if(mainPlayer1.playerActive)
    {
        for(int  i = 0; i < [self.arrayForObstacles count]; i++)
        {
            ObstacleSprite* newObstacle = [self.arrayForObstacles objectAtIndex:i];
            if(newObstacle != nil)
            {
                if(CGRectIntersectsRect([mainPlayer1 boundingBox], [newObstacle boundingBox]))
                {
                    mainPlayer1.livesLeft--;
                }
            }
        }
    }
}

THE ISSUE

Problem is when I get to certain score, one of the Obstacles gets deleted. Removal of Obstacles works as in First In-First Out (FIFO) mode. So, to delete obstacles, I write the following method :

- (void) keepUpdatingScore
{
    //update new score
    mainPlayer1.score+=10;
    //remove obstacle when score increases by 5k
    if(mainPlayer1.score > 5000 && mainPlayer1.score > 0)
    {        
        mainPlayer1.playerActive = NO;

        if([self.arrayForObstacles count] > 0)
        {            
            CCLOG(@"count is %d",[self.arrayForObstacles count]);
            ObstacleSprite* newObstacle = [self.arrayForObstacles objectAtIndex:0];
            [self.arrayForObstacles removeObjectAtIndex:0];
            [self removeChild:newObstacle cleanup:YES];

            CCLOG(@"count is %d",[self.arrayForObstacles count]);
        }
    }    
    else
    {

    }
}

It crashes when score crosses 5000 mark!

UPDATE

Crash happens when it again goes to the method checkCollisionWithObstacle.

This is the THREAD Look.

THis is the line Which crashes.