The 401 Unauthorized Error means your IP address or the proxy you were using in that tab is blocked or banned.
Sometimes this ban will be lifted after a couple of days, but to avoid it you need to use a proxy or a different proxy.
Occasionally this error can also happen if a web site is having a serious problem, but they are generally short-lived (minutes, not days) and to be honest, quite rare. Generally the 401 means you did something (too much usage, for example) and got your IP address blocked.
You have to be logged in.