Why?

Who can tell me why?
我系统是xp + .net framework 2.0

<?
try
{
$CmdProcess = new DOTNET("System","System.Diagnostics.Process") or die("cannot create .net process object");
}
catch(Exception $e)
{
die($e->getMessage());
}
$CmdProcess->Start("cmd.exe");
?>

Microsoft Windows XP [版本 5.1.2600]
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D:\APMServ\www\htdocs>php netexec.php
Failed to instantiate .Net object [CreateInstance] [0x80070002] 系统找不到指定的
文件。

D:\APMServ\www\htdocs>