This machine works. smb.conf:

[global]
    workgroup = Home
    netbios name = web_server
    server string = %h server (Samba %v)

[www-docs]
    path = /home/robinhoode/www
    comment = Documents for web server
    read only = no
    valid users = robinhoode

This one doesn't. smb.conf:

[global]
    workgroup = Home
    netbios name = music_server
    server string = %h server (Samba %v)

[mp3]
    path = /mp3
    comment = Mp3 files
    read only = no
    valid users = robinhoode