Thank you for these links,

From what I have read it could be a number of things.

Would you suggest not moving him from the cage to his box, as one of those states that they do not become aggressive if you feed them in their cage.

I personally have always suspected that the temperature in his cage / the humidity is too low, but currently we do not have anything to measure this, we do have one of those heaters that stick to the underside of the cage, but it is not very big. I will try to obtain a digital thermometer today, if I can afford it. (Petland likes to jack their prices) (No we didnt get the snake from petland, it was from a reptile store that breeds them)