エクスポート クラスを使用すると、jpgraph chart がチャートを出力できません

<?php // content="text/plain; charset=utf-8"<br />require_once ('SqlHelper.class.php');//这是我写的类，用于操作数据库，但是一引入就出错<br />require_once ('jpgraph/jpgraph.php');<br />require_once ('jpgraph/jpgraph_bar.php');<br /><br /><br />$datay1=array(12,12,15);<br />$datay2=array(0,0,0);<br /><br />// Create the graph.<br />$graph = new Graph(350,250);<br />$graph->SetScale('textlin');<br />$graph->SetMarginColor('silver');<br /><br /><br />// Setup title<br />$str="";<br />$id=$_REQUEST['id'];<br />if($id==1){<br />	$str="支持布什的情况统计图";<br />}else if($id==2) {<br />	$str="支持奥巴马的情况统计图";<br />}<br />$graph->title->Set($str);<br />$graph->title->setFont(FF_SIMSUN,FS_BOLD,14);<br />// Create the first bar<br />$bplot = new BarPlot($datay1);<br />$bplot->SetFillGradient('AntiqueWhite2','AntiqueWhite4:0.8',GRAD_VERT);<br />$bplot->SetColor('darkred');<br /><br />// Create the second bar<br />$bplot2 = new BarPlot($datay2);<br />$bplot2->SetFillGradient('olivedrab1','olivedrab4',GRAD_VERT);<br />$bplot2->SetColor('darkgreen');<br /><br />// And join them in an accumulated bar<br />$accbplot = new AccBarPlot(array($bplot,$bplot2));<br />$graph->Add($accbplot);<br /><br />$graph->Stroke();<br />?><br />