Welcome Davie,
Thank you for reaching out to Microsoft Q&A.
I understand that Windows Live Mail displays a sign-in error even though you can still send and receive emails.
Please note that Windows Live Mail reached end of support on January 10, 2017, but you can still try some workarounds.
To better understand your issue, could you please clarify:
- Does the sign-in error appear immediately when you open Windows Live Mail, or only when you click "Sign in"?
- Are you using Windows Live Mail 2012, and is your computer running Windows 10 or Windows 11?
- Does the error appear only for your Ntlworld accounts, or does it also appear when signing in with your Microsoft account?
Since sending and receiving emails still works, I would like to identify which sign-in process is affected before suggesting further steps.
I look forward to your response.