Natwest and RBS customers have been left unable to log into their online banking this morning.
The banking giants encouraged their customers to update their apps - but now people have been left unable to log into their accounts, despite updating their app.
People are complaining this morning on social media that they can't log in, check their balance or transfer money.
Some customers are also having trouble accessing NatWest's business service - Bankline - which means they are unable to process payments to their staff.
Natwest has been advising on social media to clear browser cookies if they are trying to access via desktop.
And those who complained about the issues with the app update on Twitter were told to delete the app and reinstall it.
An RBS spokesman told This is Money: "We have just released the latest version of our mobile app.
"For a small number of customers after downloading the latest version they may have received an error message. If this has happened we'd recommend fully uninstalling the app and downloading it again."
