Confusing message on attempting to register new account with upper case

[markw]

On registering a new account, if you try to use a capital letter in your 'Login', you get the unhelpful error message:

"The form contains invalid entries: Name: Url must be purely lowercase alphanumeric (ascii) characters and these symbols: -_"

What does 'Name' or 'Url' have to do with anything? It means 'Login must be ...'

But even better would be to make the login case-insensitive and allow capitals to be entered.