Allied Irish Banks is refunding more than €8 million to bank customers who were mistakenly billed for ATM transactions they did not make.
AIB says that following a review of unsuccessful ATM cash withdrawals it is to refund €5.1m relating to 41,000 AIB customer transactions and €3.2m relating to 30,000 non AIB Bank customers.
The refund relates to cases where a customer's account was debited for a cash withdrawal even though the customer did not take the money which was dispensed by the ATM.
The problem - which ran over a seven-year period - arose as a result of the introduction of anti-fraud measures which prevented the automatic processing of refunds for these particular transactions.
AIB says process and procedure changes have now been put in place to prevent a reoccurrence.
An AIB spokesman told the Belfast Telegraph that an undisclosed donation will also be made to charity in lieu of several unidentified customers whose accounts were debited as far back as 1995.
It's not the first time AIB has experienced problems with its cash machine network. In February 2009, the bank apologised to customers after a malfunction double-debited cash withdrawals from consumer accounts.