Incorrect bank balances, declined cards and missing wages were all reported by shocked Halifax and Bank of Scotland customers today.
The banks were inundated with phone calls from concerned customers when a technical error led to delays in payments being made and received.
But the problem - which only affected debits and credits conducted overnight - has been corrected and all delayed transactions have now been processed.
A Halifax spokesman said: "Due to a technical error overnight, we experienced a slight delay in processing debits and credits for Halifax and Bank of Scotland customers.
"We have already corrected the problem and all delayed transactions have now been processed. This has only affected transactions that were due to be processed through the night.
"We worked to fix the problem swiftly. We are extremely sorry for the inconvenience this will have caused customers early this morning, but this has now been resolved."
The banking blunder comes a day after Spanish giant Santander said it had sent bank statements for up to 35,000 customers to the wrong addresses.