Ubuntu File Server, Permission Problems !

I have a remote file server running Ubuntu 10.04 but really and (I mean REALLY) struggling in getting the permissions set correctly..

I have users A,B,C,D.
User A is in groups admin and lxusers.
Users B,C,D are in the group lxusers.

I have a root share called 'Shared Folder' currently owner root & group is admin.  I want users to be able to create sub folders and files inside 'Shared Folder'. The user that creates folders and files will be the owner and those folders and files they create will inherit the parents group of admin. I only want the owner & members of the admin group to be able to delete any of the folders or files created, I am happy enough for any of the lxusers group to read anything thats created by any user.

This so far appears to be working to a point, but I do have one problem that is causing me real grief. If any user in the lxusers group creates a folder then files inside that folder, other users can delete the files but not the folder.. Just can't work out where I have gone wrong, advice to resolve would be appreciated..

Entry in smb.conf:-

[Shared Folder]
      browseable = yes
      writeable = yes
      invalid users = root
      path = /mnt/raid/Shared
      comment = Shared folder for All Users
      valid users = @admin,@lxusers
        create mode = 0774
        directory mode = 0774
        force group = admin

Kind Regards

John
DirPermissions.jpg
FilePermissions.jpg