- Start - Run (Search for programs) - gpedit.msc - Enter to start the Group Policy Editor.
- Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options\Accounts: Limit local account use of blank passwords to console logon only.
- Double click on Account:Limit local account use of blank passwords to consol logon only
- Choose Disabled, and OK.
NOTE: By default, this policy is on (enabled).
Source : http://support.microsoft.com/default.aspx?scid=303846