This message appears, when you did resetyour password as an example.
You have to enter the key that the client gave you after first login. That you hopefully wrote down.
Just click on the message or the status bar icon to open the Recovery dialog.
Without the key you must use fallback to reset your account. This will clear your account items (Bookmarks & identities) and the client generates a new key
The client will upload the current cached items into your account.
