Hi,
I tried to add a UK address but it said "There are some errors on this page." but nothing was highlighted as being an error.
I got around it by temporarily changing my country to USA which then exposed the state/province box with an error saying it was mandatory or something like that. I picked a random state and then switched my country back to UK and was then able to add my address.
I was also unable to add a UK credit card before I did this (it just showed an error and asked me to reload the page every time).