I had the same pb, and as a big noob in computers, i solve it like by magic lol.
I had ZoneAlarm, that i shut down to go back to the windows firewall to follow the tutorial : it was working well in my computer browser, but not on my ipad 2.
So as I thought i would not working, i went back to zonealarm, and hop, it works !
Don't ask me why, it works now, that's all i need to know :)
(note : it started to run when having the preview not working on my ipad, just after i closed chrome on my pc. Maybe the ipad need to have at the 1st time a kind of full access, i don't know. After that, it works perfectly on both :) Yoo hoo !)