Picture posting is enabled for all :)
Goodlife, maybe the lesson is that correct hardening of plants can make a big difference to their cold tolerance. Also, I have read that plants grown in high nitrogen-available soil are more prone to frost/cold damage, so maybe your seedlings had used up the nitrogen from the compost, and had been lucky enough to experience ideal progressive hardening, while those in the greenhouse were pampered and soft, then were suddenly chilled.