Grant User Firebird

public function PermissoesUsuario($Banco, $Usuario){
        global $admin;
        $return = "";
        try{
            $cnx = $this->conectar($Banco, $admin["USUARIO"], $admin["SENHA"]);
            if (!$cnx){
                $cnx = $this->conectar($Banco, $admin["USUARIO"], $admin["SENHA"]);
                throw new Exception("# Nao foi possivel retornar conexao.");
            }

            $sql = " SELECT RDB\$RELATION_NAME AS TABELA
                     FROM RDB\$RELATIONS R
                     WHERE RDB\$SYSTEM_FLAG = 0
                     AND   NOT EXISTS(SELECT *
                                      FROM RDB\$USER_PRIVILEGES P
                                      WHERE P.RDB\$RELATION_NAME = R.RDB\$RELATION_NAME
                                      AND   P.RDB\$USER = '".$Usuario."'
                                      )
                     ORDER BY RDB\$RELATION_NAME ";
            $resultado = ibase_query($cnx, $sql);
            $tr = ibase_trans();
            while ($row=ibase_fetch_object ($resultado)){
                if ($Usuario == "ADM"){
                    $sql= " GRANT ALL ON ".$row->TABELA." TO ".$Usuario." WITH GRANT OPTION";
                }else{
                    $sql = "GRANT SELECT, INSERT, DELETE, UPDATE, REFERENCES ON ".$row->TABELA." TO ".$Usuario." WITH GRANT OPTION";
                }
                $query = ibase_prepare($tr, $sql);
                $tmp = ibase_execute($query);
                //$tmp = ibase_query($tr, $sql);
                echo "result sql: ".$tmp."<br>";
            }
            ibase_commit($tr); // <- precisa do $tr aqui
            ibase_close($cnx);
        }catch (Exception $ex) {
            echo "erro rollback: ".$ex->getMessage()."<br>";
            ibase_rollback();
            $return = "#".$ex->getMessage();
        }
        echo "fim<br>";
        //exit;
        return $return;
    }