Since 19th April 2013, credit cards or bank cards issued by Mastercard brands are not possible to withdraw money from ATM in Japan.
This case only applied to the cards issued outside of Asia/Pacific region + the Netherlands+Canada.
I personally experienced this situation a couple of days before. So just be prepared to have a VISA card for example, to avoid this situation!
Futher information you can read by the follwing links. Unfortunately, there is no exact date when they will solve this issue.
http://www.jp-bank.japanpost.jp/en/ias/en_ias_index.html
http://www.mastercard.com/jp/personal/jp/cardholderservices/atmlocations/notification.html