Por padrão, as contas sem senhas são impedidas de fazer login via área de trabalho remota (elas são limitadas apenas a logins de console). Você pode substituir isso seguindo as etapas abaixo:
To configure the Remote Desktop host computer to accept user name with blank password, go to Control Panel -> Administrative Tools (Under System and Maintenance in Windows Vista) -> Local Security Policy. Alternatively, run GPEdit.msc (Group Policy Editor).
Then, expand Security Policies -> Local Securities -> Security Options (for user using Group Policy Editor or GPEdit.msc, expand Local Computer Policy -> Computer Configuration -> Windows Settings -> Security Settings -> Local Policies -> Security Options). Locate Accounts: Limit local account use of blank passwords to console logon only policy, and set its value to Disabled.