After successful samba sharing already few days ago I have the same thing today yet I have received the following error:

'net usershare' returned error 255: net usershare add: cannot convert name "Everyone" to a SID. 

The connection was refused. Maybe smbd is not running.

When trying to start/restart samba service I get the following

$ sudo service samba status

 * nmbd is running

 * smbd is not running

$ sudo service samba start

$ sudo service samba restart

$ sudo service samba status

 * nmbd is running

 * smbd is not running

My /var/log/samba/smbd.log

[2014/01/15 16:21:46,  0] smbd/server.c:1072(main)

  smbd version 3.6.18 started.

  Copyright Andrew Tridgell and the Samba Team 1992-2011

[2014/01/15 16:21:46.426302,  0] smbd/server.c:1128(main)

  standard input is not a socket, assuming -D option

[2014/01/15 16:21:46.428538,  0] auth/auth_util.c:708(get_guest_info3)

  SamInfo3_for_guest: Unable to locate guest account [guest]!

[2014/01/15 16:21:46.428578,  0] smbd/server.c:1251(main)

  ERROR: failed to setup guest info.

My /etc/samba/smb.conf

$ grep -E "^[^#;].*" /etc/samba/smb.conf

[global]

   workgroup = WORKGROUP

   server string = %h server (Samba, Ubuntu)

   dns proxy = no

   log file = /var/log/samba/log.%m

   max log size = 1000

   syslog = 0

   panic action = /usr/share/samba/panic-action %d

   encrypt passwords = true

   passdb backend = tdbsam

   obey pam restrictions = yes

   unix password sync = yes

   passwd program = /usr/bin/passwd %u

   passwd chat = *Entersnews*spassword:* %n

 *Retypesnews*spassword:* %n

 *passwordsupdatedssuccessfully* .

   pam password change = yes

   map to guest = bad user

        usershare allow guests = yes

        username map = /etc/samba/smbusers

        security = user

        guest ok = yes

        ; guest account = nobody

  usershare max shares = 100

  usershare owner only = False