Hey Alan,
Check that drive letter G isn't already reserved. I notice that your data drive is D and I would guess that your optical drive is E or F. That does not leave much of a margin if you have a flash drive or external drive plugged in as well. You might want to choose a higher letter for the virtual drive to avoid possible conflicts.
Also, as Adultry commented, the latest version of the plugin is 1.2.2, not 1.2.1. Best to be on that version before posting new files. You can get it through his link a couple posts above.