I wonder if the looming possibility of a Japanese bank bail-in is causing this.
http://finance.yahoo.com/news/japan-adopt-bail-ins-force-181947896.htmlMaybe Gox is working to secure other bank accounts, though one would have hoped Gox would already have had backup accounts in place.
Or maybe the bank turned its API off to keep USD from fleeing on news of the bail-in. They simply told Gox it was "broken."
I don't know how large this bank that MtGox uses is but is it possible that mass withdrawals from MtGox have in fact created a run on their bank ?