[Samba] Can't join to Domain

[basti]

Hello,
yesterday I setup a AD DC.
Today I try to add a Fileserver to the AD.

https://wiki.samba.org/index.php/Idmap_config_ad

smb.conf:

[global]

	security = ADS
	workgroup = NET
	realm = NET.EXAMPLE.COM

	log file = /var/log/samba/%m.log
	log level = 1

	# Default ID mapping configuration for local BUILTIN accounts
	# and groups on a domain member. The default (*) domain:
	# - must not overlap with any domain ID mapping configuration!
	# - must use a read-write-enabled back end, such as tdb.
	idmap config * : backend = tdb
	idmap config * : range = 3000-7999
	# - You must set a DOMAIN backend configuration
	# idmap config for the NET domain
	idmap config NET:backend = ad
	idmap config NET:schema_mode = rfc2307
	idmap config NET:range = 10000-999999
	idmap config NET:unix_nss_info = yes

	vfs objects = acl_xattr
	map acl inherit = yes
	store dos attributes = yes

[homes]
    comment = Home Directories
    browseable = no

root at fs:/var/lib/samba# cat /etc/krb5.conf
[libdefaults]
	default_realm = NET.EXAMPLE.COM
	dns_lookup_realm = false
	dns_lookup_kdc = true
root at fs:/var/lib/samba#

root at fs:/var/lib/samba# net ads join -U Administrator
Password for [NET\Administrator]:
Failed to join domain: failed to lookup DC info for domain 
'NET.EXAMPLE:COM' over rpc: Indicates the SID structure is not valid.

DNS also works as expected.
All tests done on 
https://wiki.samba.org/index.php/Setting_up_Samba_as_a_Domain_Member are OK