You can find your ISO Country code by visiting this web site 
 
http://www.iso.ch/iso/en/prods-services/iso3166ma/02iso-3166-code-lists/list-en1.html 
 
For quick reference the United Kingdom country code is 'GB' NOT 'UK'

Using UK as your ISO Country code in your CSR will cause the validation to fail. If you live in the United Kingdom be sure to use GB