I had this today as well. Fixed it following this reply. You go into Hikashop - configuration - Display - Custom Fields, then open your state fiield, ensure it set as type 'Zone'. You can also rename the drop down as County and set a 'select a value in the list':
That's because you unpublished all the other countries but you didn't save the country custom field's new default value.
Go in the menu Display>Custom fields, edit the country field and save it with the UK as default value and it should then work properly.
Hope this helps.