Hi Gidon,
thanks for your followup.
I found the source of the problem :
1) connection to netapp was done to "Cluster-mode" and not to the "VServer".
2) I was calling "file-directory-security-ntfs-dacl-get-iter" which is the wrong one ( related to point 1 ).
3) The function "file-directory-security-get" is not available in Cluster-mode.
Solution c#:
1) connect to Vserver by calling NaServer(...);
2) api = new NaElement("file-directory-security-get");
3) api.AddNewChild("path", "Physical Path");
4) api.AddNewChild("volume-name", "VolumeXXX");
5)....
Many thanks for you your help.
Best regards
Hanna