I’m using W7-64 which seems to treat sharing differently. When I click Sharing under drive properties the Sharing button is greyed out, whereas with a sub directory it is active and allows me to select share with “everyone”. With the root drives (both of which are external USB drives) only the advanced sharing button is active but setting “everyon”e there still does not let WIIMC access it.
After searching the web, turns out you also need to add “everyone” to the security tab if it is a root drive. It now works fine.