National Australia Bank's banking system outage, which shut down services for more than a day last week and flared up again yesterday, was the result of human error at its IT systems partner IBM, according to a report. itnews reports that NAB has had an outsourcing contract with IBM since 2010, covering maintenance of its mainframes, storage and hosting, desktop fleet management, printing, service desks and operating systems.Despite the bank's rule that no production changes can be undertaken during business hours, an IBM staffer attempted a change and instead deleted "a primary DNS zone".The delay in getting services back up was due to the wait for the changes initiated to "propagate through the wider DNS," itnews reports.At 1.30pm yesterday the bank issued a statement saying customers were not able to use their cards in ATMs or payment terminals. Social media reports indicate the problem started around 11am.The latest outage also hit merchant terminals and Hicaps (medical payments) terminals. The bank directed customers to branches.Last week's outage affected mobile banking services and the internet banking platform of subsidiary UBank.