I still haven't found any solution. Have anyone of you ever had this problem? I also tried it with tdbsam backend, and I got the same error, so it's not an LDAP-related issue. I have upgraded to Samba version 3.0.30, but the problem still exists. Please help, I'm out of ideas! My original message was: I recently set up a PDC using Samba version 3.0.28a. According to the official Samba documentation, I should be able to use the Microsoft User Manager tool to manage my Samba domain controller. I am able to add/delete/modify user accounts with no problem, but editing groups is not possible for some reason. For example, if I try to add a user account to a group, I get an "Access denied" error message. This sounds a bit strange to me, since I log in to the domain as root, so privilege problems should not happen. Is this a bug or have I misconfigured something? What I have already done: - Install Samba from package - Edit smb.conf to suit my needs - Create basic group mapping with the correct RIDs (512 for domain admins, 513 for users, 514 for guests) - Create a separated directory structure for all the shares My shares are located on separate partitions, each have the user_xattr option enabled in /etc/fstab. I attached my smb.conf file to this message, to make it easier to understand my configuration. Thanks for you help in advance!