Ulster Bank customers have reacted furiously after being told their accounts may be affected for days following the latest IT glitch.
The news comes less than 24 hours after the boss of its parent company, Royal Bank of Scotland, said "robust systems had been put in place" to prevent computer foul-ups.
But in a blunder reminiscent of the 2012 debacle - which saw thousands of Ulster Bank clients locked out of their accounts for weeks - customers are now facing a financial fiasco for a fifth time.
Finance Minister Arlene Foster told the Belfast Telegraph she was "particularly concerned" about the latest crisis and urged the bank to deal with it "promptly".
Hundreds of Northern Ireland customers found their payments delayed yesterday after RBS reported that 600,000 payments went missing due to a technical fault in its IT system.
However, in an interview with this newspaper on Tuesday, RBS chief executive Ross McEwan said that the 2012 meltdown shouldn't happen again.
"You should never have your technology failing your customers," he said.
"Having had the catastrophe of 2012, we have now built a lot of resilience back into the bank, which we're very proud of."
Furious Ulster Bank customers due to have been paid yesterday, however, awoke to find the payments had not gone through, leaving some without the funds to pay bills or go about their day-to-day business.
Others reported missing social security benefits and there were problems with business accounts too.
The Finance Minister said it was "disappointing" that RBS and Ulster Bank were "once again experiencing problems processing payments".
"I am particularly concerned about the difficulties this creates for customers, particularly where this is impacting on the most vulnerable in society, such as those on benefits and low incomes," Ms Foster said.
"I understand the underlying issue has been fixed and the bank is now working to clear the backlog of payments. I urge them to do so promptly.
"When I have met with the Ulster Bank in the past, I have emphasised the importance of having robust IT systems in place and I will be monitoring this situation closely."
An Ulster Bank spokesman last night said the "issue" has been identified and fixed and promised that no customers would be left out of pocket.
"We are working flat out to get these payments updated for our customers no later than Saturday," he said.
"To any customers concerned about the implications of this issue we advise them to come into a branch or get in touch with our call centres where our staff will be ready to help."
PR executive Leanne Reilly, from Belfast, told this newspaper she was worried about not having money for her holiday in Croatia next week.
"I'm an Ulster Bank customer and my boyfriend is with RBS, so it's a double whammy for us," she said.
"I usually book my currency online but I've been told not to do anything while this is ongoing.
"We have savings in RBS but there are no branches here so we can't go into the bank and get money, which means we may not have any Kuna to take with us.
"Croatia accepts euros but we've been warned it won't be value for money if we're spending it there due to charges and the exchange rate."
The 30-year-old freelance said she was fed up with Ulster Bank after being with it for 11 years.
"As a customer I'm used to this type of thing, but it has got to the stage that I'm very unhappy with the bank," she said.
"It's the fifth time I've been affected by their IT problems but this is the worst because I haven't been on holiday for five years.
"My boyfriend and I will be switching banks when we come home."
Belfast civil servant Paul Turner (50), an Ulster Bank customer of 16 years, was having problems with transfer payments.
"In a world of instant everything, to be told you can't have access to your own money is inexcusable," he said.
"I have a business account and a current account with them, as well as my mortgage, but this might be enough to make me switch.
"No other business sector would get away with this level of ineptitude."
Brian McClelland (48), from Tandragee, said he hadn't received his housing benefit payment.
"It's a flaming disgrace that this keeps happening over and over again to Ulster Bank customers," said the self-employed businessman.
"I'm leaving as soon as possible. I've had enough."