Nationwide has apologised to thousands of customers in Northern Ireland after money they withdrew from cash machines was not debited from their accounts.
About £400,000 was not debited from customers' accounts
The error affects more than 7,500 people and involves a total of £400,000 which was taken out of Northern Bank ATMs between November and February.
Customers will now have the money debited from their account on 10 March.
Nationwide said overdrawn customers will not be charged. The error came to light after a customer complained.
Customers have been notified of the error by letter.
Nationwide has admitted the error and apologised
Jay Colville, area director of Nationwide in Northern Ireland, said the error was "not connected" to the upgrade of Northern Bank cash machines before Christmas.
"I would just like to apologise to all the customers affected. We do recognise it is our mistake," he said.
He said that the problem derived from an IT fault in their connection to the Link network.
"In December, the Link organisation upgraded the ATM system. Unfortunately our system didn't pick that up correctly and we apologise for that," he said.
Letters have been sent to customers from the Nationwide
"We are going to be sympathetic to hardship cases. We won't charge people for this event."
An internal investigation is now under way into what happened.
Alison Laird of the Consumer Council said they recognised that mistakes happen.
"They (the Nationwide) have given us a full briefing and that is really important because it means that when customers come to us we can help them.
"We can tell them what they need to do and how they need to respond. We can provide them with contact details for Nationwide.
"That is really important to reassure them that Nationwide will work with them to make sure that the money can go back."