Make sure there are no printer connection registry keys here:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Print\Connections
These can be from policy or have been added when running the printui tool to a a "per machine" connection.
If printui.exe or rundll32.exe calling printui.dll were used to add the printer connections data, it's best to use printui to remove the registry key.
printui.exe /? will provide syntax when using this interface.