[Samba] Permission denied on server root for all users

[mots]

Hello,

I've tried to set up a member server for my AD domain, but all users get "Permission Denied" when accessing the server, even without a share specified (by entering \\ika in Windows Explorer).
Samba version is  4.2.10-debian on Debian Jessie.

I've mapped DOMAIN\Administrator to root, which allows the Administrator to connect to the server and set permissions.
wbinfo -g and wbinfo -u lists all the users and groups.

The smb.conf on the member looks like this:

[global]
workgroup = DOMAIN
security = ads
realm = DOMAIN.COMPANY.COM
idmap config *:backend = tdb
idmap config *:range = 2000-9999
idmap config DOMAIN:backend = ad
idmap config DOMAIN:schema_mode = rfc2307
idmap config DOMAIN:range = 20001-99999
winbind nss info = rfc2307
dns proxy = no
log file = /var/log/samba/log.%m
syslog = 0
server role = member server
username map = /etc/samba/usermap
load printers = yes
spoolss: architecture = Windows x64
vfs objects = acl_xattr
map acl inherit = yes
store dos attributes = yes
[printers]
path = /var/spool/samba
read only = no
printable = yes
printing = CUPS
guest ok = yes
writable = yes
available = yes
[print$]
path = /var/fileserver/Printer_drivers
comment = Printer Drivers
writeable = yes

What am I doing wrong?
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