I'm guessing it's a leading zero problem, since all US Zipcodes are 5 digits (or...

jwn on April 11, 2012 | parent | context | favorite | on: Ziptastic: Isn't a zipcode enough?

I'm guessing it's a leading zero problem, since all US Zipcodes are 5 digits (or nine). Going to http://zip.elevenbasetwo.com/?zip=01010 gives the same response noted above.