What's the difference between "net user" and add a user through Control Panel?

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http://serverfault.com – I run a Windows 2008 server, and when I do net user XXX strong_password /ad I got a command succeed message, but unable to log on with that user and password, it kept telling me password or username is wrong. But if I do the same through Control Panel->User And Accounts, the user could log on. So what's the difference between that two methods? Or what extra steps need to take to make login possible? (HowTos)