Ulster Bank has said the backlog affecting 100,000 of its customers will not be resolved until the end of the week.
The bank said clearing the backlog was "taking significantly longer than expected" and, as a result, customer accounts would not be fully operational tomorrow. Read reaction to the Ulster Bank problems here.
While customers affected to date have mainly been those paid weekly or making one-off transactions, monthly salaries are due to be paid next week.
Ulster Bank opened branches yesterday and today to deal with customer inquiries.
The bank said it had dealt with over almost 9,000 customer telephone queries while 11,100 people had called into its branches.
A spokeswoman said the bank expected it would take until the end of the week to completely clear the backlog.
A spokeswoman said the bank expected it would take until the end of the week to clear the backlog. She was unable to give a precise estimate for the number of customers affected but said it is "well over 100,000".
“We have encountered a significant number of minor issues which require manual intervention. This has delayed us being able to move forward as quickly as we would have liked, to automatically process payments from subsequent days,” she said.
She added the bank was experiencing a “small number of interruptions” to around 5 per cent of its ATMs and some online services.
The bank stressed no customers would be “left permanently out of pocket as a result of this issue”. Today is the sixth day of disruption.
Approximately 100,000 customers in Ireland have been affected by the issue, including some 53,000 social welfare payments by Ulster Bank’s systems failure, with thousands of customers unable to receive payments.
The bank said the original technical problem was caused by a software upgrade to the payment processing system which was then corrupted.
This problem has been fixed and staff are working through a build-up of unprocessed transactions.
In some instances customers who go into branches cannot access their accounts because the bank officials cannot access them either.
However, some customers have been advanced payments based on their social welfare entitlements or their salaries.
Some 38,000 HSE employees who are paid through Ulster Bank can get an advance of up to €500.
Ulster Bank is part of the Royal Bank of Scotland group and yesterday its chief executive Stephen Hester issued a public apology and conceded the bank had let down its customers.
“I am very sorry for the difficulties people are experiencing,” he said.
“Our customers rely on us day in and day out to get things right, and on this occasion we have let them down. This should not have happened.
“This is taking time, but I want to reassure people that we are working around the clock to resolve these problems as quickly as we are able.”
"I also want to reassure customers that no one will be left permanently out of pocket as a result of this, and again, they should contact us directly about this. The bank's helpline is open until 10pm: 1800 205100