Once I have got this problem with samba in Oracle Linux 6 (the same I could reproduce in RedHat 6 as well):
On start or restart of smb service var/log/samba/log.smbd reports:
smbd/server.c:501(smbd_open_one_socket) smbd_open_once_socket: open_socket_in: Address already in use
The solution was:
sysctl net.ipv6.bindv6only=1
as it looks like the problem happens on systems which IPv6 support where :: also listens for IPv4 connections. So the bind to 0.0.0.0 fails.