很急，高手请帮忙！问题解决马上结贴

以下程序运行时为什么会出现：
error,Cannot modify header information - headers already sent by (output started at D:\webs\autowebs\ocen\admin\include\functions.php:2) in D:\webs\autowebs\ocen\usersave.php on line 15
这样的错误？请帮忙，很急，谢谢！
<?
include("./admin/include/mysql.inc.php");
include("./admin/include/config.inc.php");
include("./admin/include/functions.php");

?>
<Script language="JavaScript" src="JavaScript.js"></Script>
<?
if ($account=="" or $Pass=="" or pass!=$passcheck or $name=="" or $pid=="" or $tel=="" or $email=="" or $addr=="" or netbarname=="" )
{
$eventid=EventLog("错误","注册资料非法",$account."帐号的".$name."注册资料为密码：".$Pass." 密码确认：".$passcheck." 身份证号：".$pid." 电话：".$tel." 电子邮件：".$email,"",$account,$sessionloginip);
header("location:PageInfo.asp?InfoType=RegErr&InfoNum=$eventid");
}else{
if( SaveData())
{
$eventid=EventLog("事件","用户成功注册",$Account."帐号的".$Name."注册为本站用户","",$Account,$sessionloginip);

}else{
$eventid=EventLog("错误","注册资料非法","帐号重复 帐号：".$account." 电子邮箱：".$email,"",$account,$sessionloginip);

?>
<Script language="JavaScript">
MsgBox("该帐号或电子邮件已经存在了！！\n请换一下再试试！");
window.history.go(-1);
</Script>
<?
}
}

function SaveData($info_talbe){
global $areaid,$account,$pass,$netbarname,$name,$pid,$tel,$email,$oicq,$addr;
global $db, $card_data_user_table;
$checkstr=GetCheckStr();

$sql="Select * from $card_data_user_table where account='$account' or email='$email'";
$db->query($sql);
if($db->num_rows()>0){

$sql="insert into $card_data_user_table(areaid,account,pass,netbarname,name,pid,tel,email,oicq,addr,addtime,userflag,usercheck) values ('$areaid','$account','$pass','$netbarname','$name','$pid','$tel','$email','$oicq','$addr','curdate()','0','$checkstr')";

$SaveData=true;
}else{
$SaveData=false;
}
return $SaveData;
}
?>