The error message is indicating an incorrect password. This will be failure of password re-authentication of added secondary TalkTalk Mail accounts when added to a primary account login. Regrettably this re-authentication failure has been going on for months now and remains unfixed even though we were assured that the vendor of the mail platform was aware.
An added secondary TalkTalk email account uses the normal password that is encrypted with the primary account credentials and that encrypted password is used to authenticate the connection to the secondary TalkTalk mailbox. The authentication times out after a set period and requires re-authentication. That part of the process may or may not succeed and if it fails then you'll get the failure message.
To stop the failure messages select the downward facing chevron icon in front of all secondary added TalkTalk email account names in the left side Folder view. That will stop the attempts to load emails from the secondary added email accounts. Non-TalkTalk added email accounts will work without a problem.
Workarounds:
You can sign out of the primary account login and sign in to each secondary account individually. Obviously not as convenient as having a single sign in but there's no reason for not being able to see your emails in the secondary TalkTalk mailboxes.
Or you can add all TalkTalk email accounts to an email client like BlueMail or Thunderbird for example.
I will draw this ongoing issue to TalkTalk's attention but other than using one of the workarounds there's nothing you can change to make the re-authentication more reliable.
