It's a daytime map - so it doesn't even have any new lights placed. Just the entities.
Xplosys, thanks for the advice. I've had this problem before - done exactly that. Just a pain because all three of my computers (2 laptops and 1 pc) managed to kill themselves and I've had to restart from scratch. :/
This problem could probably do with some looking into if it's not just me. :L
Confusing.
I've run the cleaner - for other reasons - several times, so it's not anything to do with that. I've removed as much as I can without losing any of the feel to the level - a suprising amount - and it's not even increased it there. I'll get to work on dismantling it if no one has any ideas in lets say, an hour. ;/