Add group to an computer object security tab AD

[whippet]

Hi,
When you create a computer account in Active Directory (manually), you can change "The following user or group can join this computer to a domain". When you do this, the user or group is added to the security tab.

I would like to do this with c# (automatically) and I cannot find a solution.

Thank you for your help
Sorry! I'm not an english people.

[whippet]

Hi,
I receive this error message : Object reference not set an instance of an object.

My code :

DirectoryEntry computers = new DirectoryEntry( sLDAP + PCTarget, "Domain" + "\\" + "user", "Password", AuthenticationT ypes.Secure);
computers.Optio ns.SecurityMask s = SecurityMasks.O wner | SecurityMasks.G roup | SecurityMasks.D acl | SecurityMasks.S acl;

try
{
ActiveDirectory Security sdc = computers.Objec tSecurity;
NTAccount Account = new NTAccount("Doma in\\MyGroupName ");
SecurityIdentif ier Sid = (SecurityIdenti fier)Account.Tr anslate(typeof( SecurityIdentif ier));
ActiveDirectory AccessRule rule = new ActiveDirectory AccessRule(Sid, ActiveDirectory Rights.Extended Right | ActiveDirectory Rights.GenericR ead,AccessContr olType.Allow);
The message appears when the SetAccesRule is executed!!!
sdc.SetAccessRu le(rule);
computers.Commi tChanges();
computers.Close ();
computers.Dispo se();
}
catch (Exception ex)
{
MessageBox.Show (ex.Message.ToS tring());
}

Thank you