passwd, permission denied

[Marc Weber]

I'm getting this on my vserver:

[root at nixos:~]# passwd root
Changing password for root.
passwd: Permission denied


[root at nixos:~]# cat /etc/pam.d/passwd 
auth     include        common
account  include        common
password include        common
session  include        common

[root at nixos:~]# cat /etc/pam.d/common
#  auth     sufficient     /no-such-path/lib/security/pam_ldap.so 
auth     sufficient
/nix/store/22w3l41qxszyisqn09pjad8vc93kwr49-pam_unix2-2.1/lib/security/pam_unix2.so
debug
auth     required       pam_deny.so debug

#  account  optional       /no-such-path/lib/security/pam_ldap.so 
account  required
/nix/store/22w3l41qxszyisqn09pjad8vc93kwr49-pam_unix2-2.1/lib/security/pam_unix2.so
debug

#  password sufficient     /no-such-path/lib/security/pam_ldap.so 
password sufficient
/nix/store/22w3l41qxszyisqn09pjad8vc93kwr49-pam_unix2-2.1/lib/security/pam_unix2.so
debug

#  session  optional       /no-such-path/lib/security/pam_ldap.so 
session  required
/nix/store/22w3l41qxszyisqn09pjad8vc93kwr49-pam_unix2-2.1/lib/security/pam_unix2.so
debug

syslog:
Mar 18 12:26:41 nixos passwd[7919]: pam_unix2(passwd:chauthtok): pam_sm_chauthtok() called
Mar 18 12:26:41 nixos passwd[7919]: pam_unix2(passwd:chauthtok): username=[root]
Mar 18 12:26:41 nixos passwd[7919]: User root: Permission denied

strace output looks like this: http://rafb.net/p/7jq2vb43.html

Any idea how to deubg this any further?
I've exactly the same setup on a local machine which works fine?

I've even tried debugging passwd for that reason. However I can't get
debugging symbols..

I appreciate any idea which can help me finding the problem.

Sincerly
Manc Weber