The "Please enter your name" always contains a username I once entered by mistake; even though I now enter the correct one every time, the mistake gets remembered. "Please enter your password" is always blank, which is annoying because I'd expect it to be stored in the Keychain. Deleting all related Keychain entries for the network made no difference.
A quick ferret through ~/Library/ turns up a likely suspect:
me$ grep -r 'incorrect-username@domain' ~/Library/
Binary file Library/Preferences/com.apple.eap.profiles.plist matches
Opening that file up with Property List Editor and correcting all instances of incorrect-username@domain fixed the problems (including prompting for a password).