Thousands of Abbey current account customers are facing delays in receiving salaries, benefits and other funds, following a technical glitch.
The error meant payments due to be processed overnight have not been credited to people's accounts, while direct debits and standing orders supposed to leave have also not been paid.
Abbey said it had now fixed the problem, and was "urgently" processing these payments (see the Best Bank Accounts guide).
Some people have already received their payments and Abbey promised other customers the money would be in their accounts by the end of today at the latest.
It added that any direct debits and standing orders would also be paid today and customers would not incur any charges as a result. It is not known exactly how many people have been affected.
Abbey, part of Spanish banking giant Santander, has around six million current account customers, although only people expecting a credit to be paid into their account or a payment to leave it will have been affected.
Christmas salary delays
Yet a high proportion of people are likely to have been impacted as many workers receive their salaries early during December, ahead of the Christmas break.
An Abbey spokesman says: "Due to a technical error, payments due to be processed overnight have not been. We are urgently processing these.
"We apologise to customers expecting a credit and can assure them this will be in their account today.
"Any direct debits and standing orders due to go out of a customer's account today will still be paid in the normal way and no customers will incur any charges as a result of this error."
This is not the first time bank customers have been hit with delays. In both July and October, many Barclays customers were unable to access their accounts due to a system error (see the Barclays delays MSE News story).
Additional reporting by Guy Anker
Further reading/Key links
Top accounts: Best Bank Accounts
Correct bank errors: Financial Fight-Back