Is this a broadband customer account you're trying to access using the lineone.net address as Username login? Or is it a MailPlus subscription customer account? The use of lineone.net is not an issue so thanks for confirming the email account is working well.
MailPlus customers that have in the past changed their login email password cannot sign in to the MailPlus subscription customer MyAccount simply because of the in-built protections of MyAccount that do not allow a change of email address or password from a non-TalkTalk network address. And of course customers that subscribe to MailPlus are by definition not normally a TalkTalk broadband customer and therefore do not connect via a TalkTalk network address.
Heads up that there is MyAccount maintenance overnight. We don't know what this is for but try again tomorrow morning at say 9am. The current problem of lack of sign in for MailPlus customers has a lowish priority in the TalkTalk scheme of things happening and the last time TalkTalk offered a comment it was the standard phrase "We don't have a date for a fix".
Is there something particular you needed to do via MyAccount? There are workarounds for everything except creating new mailbox addresses and right now TalkTalk have withdrawn the creation of new mailbox addresses as part of the update to a newish customer interface.
