Some Lloyds TSB customers have been unable to get money from ATMs or use online customer services as a result of a system problem.
Twitter account said: "We're sorry that customers are experiencing problems with some of our services, we're looking into this & will update you as soon as we can."
Another message replying to an enquiry about when things will be fixed said: "Really sorry, we don't have a timescale, but are working to resolve the issue ASAP."
Computer Weekly contacted Lloyds and was told it had not yet put together its press statement.
The Co-operative bank is also having trouble with some customers unable to use online banking and some point of sales payments are failing.
"We are currently experiencing a temporary issue with our banking systems which has resulted in some customers being unable to access their accounts. We are working to resolve this issue as soon as possible and we would like to offer our apologies for any inconvenience caused," said a bank statement.
In July the Co-operative bank agreed to buy 632 Lloyds TSB and Cheltenham and Gloucester branches along with the millions of customers attached to them. The Co-operative said at the time that the current account customers being taken over will remain on the Lloyds Banking Group system and after a few years the Co-operative will migrate its other current account customers to the same system, which will be supported as a managed service by Lloyds TSB..
A Co-operative bank spokesperson said the problems are not related to the Lloyds TSB problems.
