I get a lot of these messages in logfile:

[2014/12/15 13:48:54.172689,  0, pid=2950] ../source3/libads/kerberos.c:926(create_local_private_krb5_conf_for_domain)
  create_local_private_krb5_conf_for_domain: smb_mkstemp failed, for file /var/cache/samba/smb_tmp_krb5.wgU6ix. Errno Permission denied

checking the owner of pid 2950:
fileserv:/var/cache/samba# ps axwu|grep 2950
root 2950 0.1 1.1 37056 11476 ? S 08:33 0:27 /usr/sbin/smbd -D

checking permissions of the directory:
ls -ld /var/cache/samba
drwxr-xr-x 4 root root 4096 Dez 15 14:23 /var/cache/samba

checking if the file already exists:
ls /var/cache/samba/smb_tmp_krb5.wgU6ix
/var/cache/samba/smb_tmp_krb5.wgU6ix: No such file or directory

checking that there are no strange ACL entries:
getfacl -s /var/cache/samba
--> no output.

when i do chmod 777 /var/cache/samba, the problems will go away, but testparm will comply that permissions need to be 755. when setting the permissions back to 755 the problems will be there again.

i have no selinux and no apparmor running.

i do not understand the problem. how can i help to debug here?