Discover IRDA Devices

I was trying to discover and list available infrared devices.
I already plug in my IRDA device and COM4 has been detected....

The code are

irDevices = irClient.DiscoverDevices(2);

The code does not show any error but it just could not detact the devices.

May i know how to check whether the devices is ready to send or receive IRDA devices?

Thanks.