I would guess that this is because Vista assumes that an ink monitor is an administrators tool.
It could be the way it's been written. If you can't allow it through the normal admin. settings, you may have to consult Minolta.
Alternatively, do away with the monitor part altogether (I've never found these to be particularly accurate or useful anyway)
My Epson has been reporting a virually empty black cartridge for about 3 month's now, and it still prints fine!