Windows XP and Windows Vista stores the value of the policy set above in a registry key named “LimitBlankPasswordUse”.
To unlock the limitation of cannot establish Remote Desktop logon with user account without a password, simply set the value data for LimitBlankPasswordUse to 0 (so that there is no limit on blank or null password use), as according to the code below. Alternatively, copy and paste the following text to a text file, and save with a .reg extension.
Then run the .reg file to merge the value to registry.