It's when the weight gets over 2kg. I need to create a workaround for that. Royal mail, that is used to calculate the shipping only transport items up to 2kg. It can be sent with other companies but it is a lot more expensive, and I'll have to create a different price for each country at various different weights. I will hopefully get to it over the next week while I'm off work
Having said that, if you want to actually buy that many puzzles, you can contact m,e for a quotew privately, I can always send a paypal invoice for the amount, but you would likely be better off making 2 separate orders, because the shipping cost jumps up dramatically over 2kg