Let’s perform some troubleshooting steps to resolve the error you’ve encountered, @l-bigwood.
To resolve this, you can clear your browser’s cache. There are times that the browser you're using has information stored that's stopping or causing the error when trying to enter employee pay details.
But first, try to use a private browser when logging into your account. If you’re able to enter pay details successfully, to use a private browser when logging into your account.
Here’s how to go incognito or use a private browser:
For Chrome, press Ctrl+Shift+N.
For Internet Explorer or Firefox, press Ctrl+Shift+P.