1 of 10 withdrawal attempts from MtGox bounces due to wrong information (wrong account number, wrong owner, wrong SWIFT address, etc), and all of the bounces have to be handled manually by their bank. This is what overloaded their old bank. They will have to work slowly through the queue to avoid too much work at once, but hopefully at a much faster pace.
This is exactly what I call a lame excuse. It sounds ridiculous for anyone who knows how a modern bank works. I can hardly imagine that you can overwhelm a bank with wire transfers. Actually, this is the way the banks make money. It is as mtgox would not let you trade because you overload their system with you trades.
So you know how a modern Japanese bank works and do international wires?
My bank is very modern I have done all my banking online since 1997 but all international wires still need manual intervention by the bank (ACK/NACK, sometimes routing). None are handled outside of normal office hours. If it bounces, they will call me if they can't find an obvious fix (they may call the receiving bank first). I would be interested to hear how this is done in Japan, since they, according to you, use a different system for international wires. Please tell us more!