1. Check your polar software for this configuration... make sure that the IR communications port is set to IrDA. Go to options > preferences and select the "hardware" tab.
Set your software to IrDA2. Check is that you have the Polar USB IrDA Infrared Adapter drivers installed. When you have installed the drivers correctly... when you in plug in the Polar IR USB stick it should be detected correctly by your computer and a red light should start flashing at the end of the Polar USB IrDA Infrared Adapter.

The IR sensor on the Polar computer is on the top left hand side. It's important to have this lined up in front of the Polar USB IrDA Infrared Adapter (facing the red flashing light).
The Polar USB IrDA Infrared Adapter If these items are correct it should all work apart from a faulty Polar USB IrDA Infrared Adapter .
I know that we have had a few problems with Polar's USB IrDA Infrared Adapter. Some just don't work. You plug them in and the red light flashes but still no connection to the watch. The only way to find out is to use a Polar USB IrDA Infrared Adapter that is known to work to test the software set-up is correct.
Anyway, Once you get it working it's very stable so you won't have to worry about it ever again.
See
http://www.pursuit-performance.com.au/polar/html/local/faq/faq_irda.html for more information.