i need to know

how can we discover IR activated devices and how can we transfer files from PC to mobile  using vb.net

Sure IrDAClient.DiscoverDevices, then use ObexWebRequest., the URL for it contains irdaAddr.ToString() as the host part.

 First of all, thank you for responding of my post

IrDAClient.DiscoverDevices is working fine
And gives device name device address and device Hints

Cool.

Well, see the samples in the user guide.  The URI format is also described in the class documentation:

Uri must use one of the following schemes - obex, obex-push, obex-ftp, obex-sync. The host name must be the device address in short hex, or dotted hex notation ...

So, something like:

IrDAClient cli = new IrDAClient();
IrDADeviceInfo[ discovered = cli.DiscoverDevices();
IrDADeviceInfo selected = f(discovered); // method 'f' has the user select a device, or just #0 (of 1 in total?!)
String uri = "obex://" + selected.DeviceAddress.ToString() + "/" + filenameWithoutPath;
ObexWebRequest req = new ObexWebRequest(new Uri(uri));
...
...

Thanks now program is working fine :)