One thing I've noticed is the devices tend to be pretty picky about access settings on the individual file shares. Since you're getting connected to the device itself, I'd recommend double-checking the permissions on each file share on the Buffalo. Also, you can check the device as a whole by just going to devicename (don't specify a share). If you see a list of folders, but can't go into any of them, it's probably a share permission issue. Adding the users themselves is kind of weird in the web interface–I recommend reloading each page to double-check that your settings 'stuck.' Also, if you're using AD groups to assign permissions and they're not working, try with just a username and move up from there.