U.S. consular posts worldwide have been experiencing delays in issuing visas due to system error and they anticipate it will take weeks to resume full visa processing capacity.
Updated information regarding processing in Japan can be obtained from the following Twitter feed: https://twitter.com/USVisaTokyo.
On July 20, the U.S. Department of State updated its visa system software to improve overall system performance and address previous performance issues. Shortly after the maintenance was performed, the database began experiencing significant performance issues. On July 23, the Consular Consolidate Database was brought back online with limited capacity. The State Department is incrementally increasing the number of processed cases the system will allow and are prioritizing immigrant visas, including adoption cases.
Additional details regarding the problem can be obtained from the State Department website: http://travel.state.gov/content/travel/english/news/ccd-performance-issues.html.