Problems with a systems integration project at Japan's Bank of Tokyo-Mitsubishi UFJ (BTMU) left thousands of customers unable to use ATMs earlier this week.
According to local press reports the software error left customers unable to complete around 20,000 transactions on Monday morning at Seven Bank cash machines, which are linked to the BTMU system.
Reports suggest the BTMU system sent a message containing an incorrect Chinese character to its Seven Bank counterpart, causing transactions to fail.
Later it emerged customers of four other banks and two brokerage firms - Japan Post Bank, Senshu Bank, Osaka Prefecture, Taisho Bank, Chukyo Bank, Okasan Securities and Nikko Cordial Securities - were unable to transfer money using Bank of Tokyo-Mitsubishi ATMs on Monday.
The bank, along with its technology supplier IBM, have been upgrading technology as part of a massive project to integrate the IT operations of Bank of Tokyo-Mitsubishi and UFJ Bank following their 2006 merger.
The bank's Web site warns customers that its ATM network will be closed down for several weekends over the next few months as the upgrade continues.