Did you create this user yourself?
It works on my XP. Professional Edition.
And the way to write it is: net user username or "user
name" new password
Note: If the username has space, you need to use quotes.
Like this:
net user "xiao mayi" abcdefgh
Check whether you have administrator privileges.
For XP
Start > Control Panel > User Accounts
Under your username, it should read "Computer Administrator".
Nothing lesser, or else you can't change.
For Vista
It won't work because users by default are not administrators.
