io ho sempre fatto così invece.....


codice:
DirectoryAttributeModification modifyUserPassword = new DirectoryAttributeModification(); 
modifyUserPassword.Operation = DirectoryAttributeOperation.Replace;
 modifyUserPassword.Name = "userPassword"; modifyUserPassword.Add("NUOVAPASSWORD");
 ModifyRequest modifyRequest = new ModifyRequest("USERNAME", modifyUserPassword); 
DirectoryResponse response = connection.SendRequest(modifyRequest);