FPDF 错误:某些数据已使用 FPDF 输出

我在尝试输出时收到 FPDF 错误

    require('cons.php');  
    $fpd = new fpdfx();
    $fpd->AddPage();
    $fpd->SetFont('Arial','B',16);
    $fpd->Cell(40,10,'Hello World!');
    $fpd->Output();

而且我的缺点代码很少.php

        error_reporting(E_ERROR | E_PARSE); //For Error Reporting        
        session_start();
        setlocale(LC_MONETARY, 'da_DK');
        set_time_limit(0);
        define("DBHOST","XXX");
        define("DBNAME","XXX");
        define("DBUSER","XXX");
        define("DBPASS","XXX");       
        define("TODAYSDATE",date('d-m-Y', strtotime("+4 months")));
        define("UPDATEDATE",date('d-m-Y', strtotime("+5 months")));       
        define("LanguageFilesURL",'XXX');   
        global $instance;
        require("inc/Email-class.php");
        require("inc/database_class.php");

类具有具有某些电子邮件功能的电子邮件功能

这是我的电子邮件类详细信息

                require("fpdf/fpdf.php");
                class fpdfx extends FPDF
                {
                }

                class Email_class
                {
                }

当我试图获得一些输出时，它的显示

FPDF 错误：某些数据已输出，无法发送 PDF 文件