THE technical failure that prevented millions of National Australia Bank customers from accessing their money or receiving pay last week continues to affect a small number of clients.

An internal document obtained by BusinessDay shows the bank is still grappling with the payments failure one week after it first emerged, plunging the bank and its customers into turmoil.

While most customer account balances are up to date, ''some residual issues are continuing to be worked through as a priority'', the bank said. The bank would not give a figure for how many are still affected, but a bank source said it was likely to be a small number.

Deposits, transfers and loan settlements are among the unresolved issues, with some customers reporting their funds have been ''lost in transit'' between accounts.

BusinessDay believes there are concerns within the bank that the problems afflicting NAB may have been caused by data loss that occurred over the weekend, as the bank frantically worked to repair the problem.