[Samba] Printing - Access Denied; no connection possible

[Lars Hanke]

I set up a new CUPS server, which works perfectly for all Linux 
machines. On the same server I installed a samba member server to allow 
for printing from Windows machines. Initial installation worked fine and 
I could print test pages from all windows systems.

Today I wanted to print from an XP machine (non-member) and it failed 
with the error given in the subject. Printing from a Win7 client 
(member) however works.

The samba server is 4.1.17-Debian (Jessie current)
This is the config as seen by testparm:

[global]
         workgroup = AD
         realm = AD.MICROSULT.DE
         security = ADS
         kerberos method = system keytab
         local master = No
         domain master = No
         winbind enum users = Yes
         winbind enum groups = Yes
         winbind use default domain = Yes
         winbind nss info = rfc2307
         winbind refresh tickets = Yes
         winbind normalize names = Yes
         idmap config AD: schema_mode = rfc2307
         idmap config AD: backend = ad
         idmap config AD: range = 1001 - 29999
         idmap config * : backend = tdb

[printers]
         path = /var/spool/samba
         printable = Yes
         print ok = Yes
         browseable = No

[print$]
         comment = Printer Drivers
         path = /srv/samba/Printer_drivers
         write list = mgr, Administrator
         create mask = 0664
         directory mask = 0775

[P6026cdn]
         path = /var/spool/samba/
         printable = Yes
         print ok = Yes
         printer name = P6026CDN

I've seen comments for older versions of samba with the recommendation 
to add "writeable=yes" to [printers]. However, if I do that and run 
testparm, the option does not show.

Can someone help with my confusion?

Regards,
  - lars.