Ah, you've found a more interesting bug. I've reported it and we'll have to look at it later. I'll mark your job as failed, so that we can try and recreate the problem. If you want, you can try and submit it again, and see if by luck it manages to complete this time. My guess is one of the items you have in the dataset is invalid for an unknown reason. We'll have to validate them individually to work out which one is the culprit.