I am talking to you, Ariba.
It's okay ... really ... to display error information when a customer person tries to login and can't. It's probably even better if this information is displayed in multiple ways. Some of us disable pop up windows and when the ONLY means you use to communicate the message "that's not a valid id" is to launch a pop-up ... we don't see it. This is frustrating. I'd much rather spend time fixing problems than diagnosing your lame customer information site.