file share issue

I've been setting up file sharing with my Mac and Win7 PC's of other members of my household. I have successfully shared my public folder and an external drive containing snapshots. When I tried to share a 2nd external drive System Preferences froze. I reboot the Mac and tried again and it freezes at the same spot, that being when I click on the + sign to add a new folder. Not the whole system, just System Preferences. I can get out of it with a Force Quit.