Royal Bank of Scotland Group Plc said some customer payments went "missing" at its consumer bank in the latest glitch after the lender was fined for a computer failure.

About 600,000 credit and direct debit transactions weren't applied to accounts, the Edinburgh-based bank said in an e-mailed statement today. While the "issue with our overnight process" and has been fixed, RBS said it's still working with affected customers to resolve any problems.

RBS was fined 56 million pounds ($88 million) by the U.K.'s Financial Conduct Authority and the Bank of England's Prudential Regulation Authority in November for the 2012 collapse of its computer system that left millions of customers without access to their accounts for weeks. The bank is spending 750 million pounds to improve its technology.

"We are working to get this resolved as quickly as possible and apologize to customers for the inconvenience caused," RBS said in the statement. "We will ensure no customers are left out of pocket as a result of this issue."

RBS shares fell 0.3% to 349.40 pence at 12:01 p.m. in London. They have declined about 11% this year.

The error affected the lender's RBS, NatWest and Ulster Bank consumer units, as well as its Coutts private bank. The bank said it's working "flat out" to get payments updated for customers affected by the failure no later than Saturday.

"Many of the payments systems in our banks are ancient," said Paul Thomalla, global head of corporate relations for ACI Worldwide, which sells payments software to banks, "They are creaking and breaking and are in urgent need of repair. This needs to be a wakeup call for the whole industry."

RBS's NatWest Help Twitter account said some customer payments were "missing" this morning. A spokesman said in an updated statement that payments "have not gone 'missing,' they have been delayed due to a technical issue which has now been fixed."

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