[Samba] Problem with pam_winbind using 'su'

[lists at zxt10d.de]

Dear list,

I installed a AD-Member Server, and now I would like to enable two users 
with local accounts to do a 'su' to AD-accounts - but that fails, the 
session is closed immediatly.

/var/log/auth.log
Apr 28 08:43:12 afpfp1 su: pam_krb5(su:auth): authentication failure; 
logname=%ADNAME%\%USERNAME% uid=1000 euid=0 tty=pts/1 ruser=%LOCALUSER% 
rhost=
Apr 28 08:43:12 afpfp1 su: pam_unix(su:auth): authentication failure; 
logname=%LOCALUSER% uid=1000 euid=0 tty=pts/1 ruser=%LOCALUSER% rhost= 
user=%ADNAME%\%USERNAME%
Apr 28 08:43:12 afpfp1 su: pam_winbind(su:auth): getting password 
(0x00000388)
Apr 28 08:43:12 afpfp1 su: pam_winbind(su:auth): pam_get_item returned a 
password
Apr 28 08:43:12 afpfp1 su: pam_winbind(su:auth): user 
'%ADNAME%\%USERNAME%' granted access
Apr 28 08:43:12 afpfp1 su: (to %ADNAME%\%USERNAME%) %LOCALUSER% on pts/1
Apr 28 08:43:12 afpfp1 su: pam_unix(su:session): session opened for user 
%ADNAME%\%USERNAME%(uid=130224) by %LOCALUSER%(uid=1000)
Apr 28 08:43:12 afpfp1 su: pam_unix(su:session): session closed for user 
%ADNAME%\%USERNAME%

Does anybody has a hint for me?

Cheers,
Torsten