I have found that the asynchronous javascript loading code to be somewhat hit and miss even locally (I use the python server which I think is single threaded and therefore probably accentuates this issue.) I can reload my working game page and have errors happen related to object classes not being defined i.e. the javascript has not been executed yet. It can also happen in cocos code itself if I specify engineDir.
I had a similar issue with my level loading code, which I resolved by having the level file itself post a cc.Notification . Is this a known issue? Fixed in next release?