If you are using the default login page, then the login is a browser-only affair. The login prompt is generated by the browser because it receives a challenge request from the web server. This type of login never complains, just repeats the same login dialog over and over again.without any message whatsoever about what went wrong last time. Nothing to be done about that.
The login prompt disappearing after the first unsuccesful attempt is another story. What Login Address were you using before the upgrade? Has it changed after the upgrade?