Can't Access Enabled Administrator Account in Safe Mode

Hello! I am running Vista Beta 2 Build 5472 and have enabled the
Administrator account in Computer Management. When I boot up to safe mode and
try to access it, however, I get the error message "The user name or password
is incorrect". This Administrator account is installed by default with no
password, so why is this happening and how can I get around it?

My steps are exactly as follows: 0) I enable the Administrator account, 1) I
boot to safe mode, 2) I see the "Administrator" and "Other User" icons on the
logon screen, 3) I select "Administrator" and see an enlarged user image and
the password field, 4) I leave the password field blank and select the blue
--> enter arrow, 5) The Welcome loading image displays for about a second or
two and then the error message appears.

Any help would be much appreciated!