Linux – Access Samba share from Windows

I have a samba share set up on a linux box which is only accessible from Windows if they turn off Microsoft network client: Digitally sign communications (always)

They would like me to configure the linux end of things to allow them to connect with this setting enabled. What is the minimum I need to do for the windows users to access this share without turning down/off any of the security options on their end?

Possibly relevant info:

• Linux box is running SLES 11 SP2 and Samba 3.6.3
• Windows box is running Windows Server 2008 with Active Directory

This is my smb.conf:

# smb.conf is the main Samba configuration file. You find a full commented
# version at /usr/share/doc/packages/samba/examples/smb.conf.SUSE if the
# samba-doc package is installed.
# Date: 2012-02-03
[global]
    workgroup = $WINDOWS_DOMAIN_NAME
    passdb backend = tdbsam
    map to guest = Bad User
    include = /etc/samba/dhcp.conf
    logon path = \\%L\profiles\.msprofile
    logon home = \\%L\%U\.9xprofile
    logon drive = P:
    usershare allow guests = No
    add machine script = /usr/sbin/useradd  -c Machine -d /var/lib/nobody -s /bin/false %m$
    domain logons = No
    domain master = No
    security = domain
    idmap gid = 10000-20000
    idmap uid = 10000-20000
    wins support = No
    wins server = 
    encrypt passwords = yes

[$shareName]
    comment = linux share
    inherit acls = Yes
    path = /home/$user/$shareName
    read only = No
    available = yes
    browseable = yes
    public = yes
    writable = yes

When they attempt to access the share currently, the errors in /var/log/messages are like:

linux smbd[3336]: [2014/01/24 11:23:25.214046,  0] rpc_client/cli_pipe_schannel.c:54(get_schannel_session_key_common)
linux smbd[3336]:   get_schannel_session_key: could not fetch trust account password for domain '$WINDOWS_DOMAIN_NAME'
linux smbd[3336]: [2014/01/24 11:23:25.216148,  0] rpc_client/cli_pipe_schannel.c:184(cli_rpc_pipe_open_schannel)
linux smbd[3336]:   cli_rpc_pipe_open_schannel: failed to get schannel session key from server $DOMAIN_CONTROLLER for domain $WINDOWS_DOMAIN_NAME.
linux smbd[3336]: [2014/01/24 11:23:25.219196,  0] auth/auth_domain.c:193(connect_to_domain_password_server)
linux smbd[3336]:   connect_to_domain_password_server: unable to open the domain client session to machine $DOMAIN_CONTROLLER. Error was : NT_STATUS_CANT_ACCESS_DOMAIN_INFO.