Scene changing after closing

[PGD]

So lastnight I got to the position you can see in the top render. Open the same file today, re-render and now it looks liek the bottom image - WFT!?

What's going on there then, why would the scene do that and do we have any ideas on how to get it back?

[PGD]

It seems the ies lights corrupted, once I changed the ies type they started working again. However it took some time to balance the light and exposure again, which I could have done without. One of those things I guess.