It looks like a chuck was generated with different settings to the rest of the world (possibly because I was using customised world generation settings)
This was in a new world, only just generated, and not saved / reloaded (before I saw the chunk error)
Ive attatched the world, just incase you need any of the customised world settings or anything
[media]
Sure this is the same issue as MC-315?
I don't think ive had any other worlds with the same name...