samba - Mar 2009 - directory permission - access denied

When I try to write to my directory, it says: access denied.

smb.conf (v3.0):

[global]
        workgroup = AD
        security = ADS
        realm = AD.COMPANY.COM
        encrypt passwords = yes
        preferred master = no
        log level = 3
        auth methods = winbind
        winbind enum users = yes
        winbind enum groups = yes
        winbind use default domain = yes
        idmap uid = 100000-200000
        idmap gid = 100000-200000
        netbios name = test
        password server = 192.168.25.25
        template homedir = /home/%D/%U
        template shell = /bin/bash
        winbind enum groups = Yes
        winbind enum users = Yes

[mkt]
        path = /mkt/
        comment = mkt Data Share
        directory mask = 0770
        read only = no
        available = yes
        browseable = yes
        writable = yes
        guest ok = no
        public = no
        printable = no
        share modes = no
        locking = no

The directory /mkt/ has 775 permission and is owned by root and group
mkt (I added group using the groupadd command). In /etc/group I have
added active directory user to the mkt group.

Now I log on to Windows using AD user name and password and mount
\\server\mkt and it doesn't ask for any user name and password. I then
try to create a file and it says denied.

I can log on using my AD account with smbclient ( smbclient
\\\\server\\mkt -U AD_USER_NAME)

I can see the shares using  smbclient -L server -U <AD_USER_NAME>

Thanks for any help.