Help! Cannot get Samba to work!

I am having a nightmare getting a new Solaris server to join a domain in order to access some samba shares.

[global]
	workgroup = OURDOMAIN
	realm = INTERNAL.OURDOMAIN.COM
	server string = Maginus SUN2014, Samba %v
	interfaces = 172.XX.X.X
	security = ADS
	password server = *
	server signing = auto
  	client signing = auto
	map to guest = Bad Password
	guest account = web
	preferred master = Auto
	wins server = 172.XX.X.X, 172.XX.X.X, 172.XX.X.X
	idmap uid = 10000-20000
	idmap gid = 10000-20000
	template shell = /bin/bash
	winbind enum users = Yes
	winbind enum groups = Yes

[home_report]
	comment = Home Report for Res Bulk Pick Lists
	path = /home/report
	guest only = Yes
	guest ok = Yes

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krb5.conf

[libdefaults]
        default_realm = INTERNAL.OURDOMAIN.COM

[realms]
        INTERNAL.OURDOMAIN.COM = {
                kdc = DC1.INTERNAL.OURDOMAIN.COM
                kdc = DC2.INTERNAL.OURDOMAIN.COM
                kdc = DC3.INTERNAL.OURDOMAIN.COM              
                admin_server = DC1.INTERNAL.OURDOMAIN.COM
        }

[domain_realm]
	OURDOMAIN = INTERNAL.OURDOMAIN.COM

[logging]
        default = FILE:/var/krb5/kdc.log
        kdc = FILE:/var/krb5/kdc.log
	kdc_rotate = {

# How often to rotate kdc.log. Logs will get rotated no more
# often than the period, and less often if the KDC is not used
# frequently.

		period = 1d

# how many versions of kdc.log to keep around (kdc.log.0, kdc.log.1, ...)

		versions = 10
	}

[appdefaults]
	kinit = {
		renewable = true
		forwardable= true
	}
	gkadmin = {
		help_url = http://docs.sun.com:80/ab2/coll.384.1/SEAM/@AB2PageView/1195
	}

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Every time I try the net ads join -U administrator command, I get:

# net ads join -U administrator
Enter administrator's password:
[2014/09/25 08:29:27.672173,  0] libads/kerberos.c:333()
  kerberos_kinit_password administrator@INTERNAL.OURDOMAIN.COM failed: Preauthentication failed
Failed to join domain: failed to connect to AD: Preauthentication failed

I am a newbie to unix/samba and I am learning as I go, so your help is appreciated!