Using: Delphi 2010 and the JEDI Windows API and JWSCL

I am trying to assign the Logon As A Service privilege to a user using LsaAddAccountRights function but it does not work ie. after the function returns, checking in Group Policy Editor shows that the user still does not have the above mentioned privilege.

I'm running the application on Windows XP.

Would be glad if someone could point out what is wrong in my code:

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, JwaWindows, JwsclSid;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

function AddPrivilegeToAccount(AAccountName, APrivilege: String): DWORD;
var
  lStatus: TNTStatus;
  lObjectAttributes: TLsaObjectAttributes;
  lPolicyHandle: TLsaHandle;
  lPrivilege: TLsaUnicodeString;
  lSid: PSID;
  lSidLen: DWORD;
  lTmpDomain: String;
  lTmpDomainLen: DWORD;
  lTmpSidNameUse: TSidNameUse;
  lPrivilegeWStr: String;
begin
  ZeroMemory(@lObjectAttributes, SizeOf(lObjectAttributes));
  lStatus := LsaOpenPolicy(nil, lObjectAttributes, POLICY_LOOKUP_NAMES, lPolicyHandle);

  if lStatus <> STATUS_SUCCESS then begin
    Result := LsaNtStatusToWinError(lStatus);
    Exit;
  end;

  try
    lTmpDomainLen := DNLEN; // In 'clear code' this should be get by LookupAccountName
    SetLength(lTmpDomain, lTmpDomainLen);

    lSidLen := SECURITY_MAX_SID_SIZE;
    GetMem(lSid, lSidLen);
    try
      if LookupAccountName(nil, PChar(AAccountName), lSid, lSidLen, PChar(lTmpDomain),
        lTmpDomainLen, lTmpSidNameUse) then begin
        lPrivilegeWStr := APrivilege;

        lPrivilege.Buffer := PChar(lPrivilegeWStr);
        lPrivilege.Length := Length(lPrivilegeWStr) * SizeOf(Char);
        lPrivilege.MaximumLength := lPrivilege.Length;

        lStatus := LsaAddAccountRights(lPolicyHandle, lSid, @lPrivilege, 1);
        Result := LsaNtStatusToWinError(lStatus);
      end
      else
        Result := GetLastError;
    finally
      FreeMem(lSid);
    end;
  finally
    LsaClose(lPolicyHandle);
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  AddPrivilegeToAccount('Sam', 'SeServiceLogonRight');
end;

end.

Thanks in advance.