The default location is set relative to the FMHome directory (the FM installation directory)...
Can you change the setting to another relative location within the FM installation directory?
Can you create a folder on your D drive and then map to that specific folder, rather than the root drive itself?
It may make no difference, but did you try
I've set maker.ini to external drives and network locations before (for template locations and for site dictionaries), so if you're still having issues, I'd look to your other systems and permissions for clues.
One other thing: Have you tracked down the Customizing FrameMaker PDF file?
Although a v7 file, it may shed light on what you're trying to do.
Message was edited by: mattrsullivan