Replying to NS shop

alright so im trying to buy some shirts from the NS online shop and everytime i go to checkout, this appears:


This is currently the only shipping method available to use on this order. North American Shipping  The shipping rate cannot be determined at this time

and i cant go on with the purchase of my stuff.
does anybody know whats wrong or how i can fix it?
because yesterday, this didnt happen
+k for any help?