Specified serial port is not valid in php_serial.class.php for windows

I've tried to connect the NV200 smart payout device to my php project using php_serial.class.php, but got this error:

Specified serial port is not valid in D:\xampp-7\htdocs\testsocket\php_serial.class.php on line 145

II'm using windows 7 and checked into device manager, the device is connected to COM3. This is my code:

include "php_serial.class.php";
$serial = new PhpSerial;

$serial->deviceSet("COM3");

$serial->confBaudRate(2400);
$serial->confParity("none");
$serial->confCharacterLength(8);
$serial->confStopBits(1);
$serial->confFlowControl("none");

$serial->deviceOpen();

$serial->sendMessage("Hello !");

What have gone wrong? What is the proper way to connect to serial port? Please help.