Ulster Bank says "human error" is to blame for its latest blunder which means some customers' balances are appearing incorrect.
Some say their cards have been declined, and lodgements aren't showing up, while others are incorrectly overdrawn.
The bank says any transactions not showing properly since Friday will be fixed overnight.
“As a result of human error, a payment file did not process last night, which means that some transactions applied to some customers accounts since 20th April are temporarily not showing", an Ulster Bank spokesperson said.
"We investigated this issue as a matter of urgency and have already taken the necessary corrective action which will see recovery actions overnight.
Ulster Bank has apologised and promised no customer will be left out of pocket as a result of the issue.
Affected customers can contact the bank to arrange emergency cash.