Unexpected End of Stream

Em client worked without fault until Sunday but now reports an Authentication failure due to "Unexpected end of stream.  Log and screen shot below:

06:54:57 xxx@tiscali.co.uk [SMTP]  Connecting: To xxx@tiscali.co.uk

06:54:58 xxx@tiscali.co.uk [SMTP]  MailExceptions.LoginException: The authentication failed due to the following reason:
06:54:58     "Unexpected end of stream.
06:54:58    at MailClient.Smtp.SmtpSendCommand.Authenticate(WorkerStatus status)
06:54:58    at MailClient.Smtp.SmtpSendCommand.Connect(WorkerStatus status)
06:54:58    at MailClient.Smtp.SmtpSendCommand.Execute(WorkerStatus status)
06:54:58    at MailClient.Commands.Command.Process(WorkerStatus status)

Hello Mike,
are you using windows firewall or any antivirus software? Please check if either of these isn’t blocking the connection by temporarily turning them off or making an exception for eM Client inside of them.

Regards,
Olivia

With no apparent changes to my setup to cause this problem, it has now gone away without any changes to fix it!

Problem gone.

Thanks.