CCTMXLayer * CCTMXTiledMap::layerNamed(const char *layerName)
    {
        std::string sLayerName = layerName;
        if (m_pChildren && m_pChildren->count()>0)
        {
            CCTMXLayer *layer;
            NSMutableArray::NSMutableArrayIterator it;
            for (it = m_pChildren->begin(); it != m_pChildren->end(); ++it)
            {
                layer = (CCTMXLayer*)(*it);
                if (layer && layer->getLayerName() == sLayerName)
                {
                    return layer;
                }
            }
        }

        // layer not found
        return NULL;
    }

In these lines:

layer = (CCTMXLayer*)(*it);
if (layer && layer->getLayerName() == sLayerName)

The developer add in a child which isnot the type of CCTMXLayer*, so the program crashs at getLayerName()