Originally Posted by ifox

I had exactly same problem on my Vista laptop. The first thing to check is if there any other software that may interfere with PowerAgent. It could be something like Windows ActiveSync.

In my case there were no interference with another software. PowerAgent was showing new COM port (COM11) but was unable to find PowerTap on it. You can find this information in Edit -> Application Settings -> Preferred Device Port. The default setting in the drop-down list is "Automatically detect port". Keep it this way, but if you open the list you'll see available COM ports.

Here is what I ended up doing to resolve the problem:

1) connect PowerTap's cradle to a USB port. There's no need to attach Powertap itself, but it won't hurt.
2) open Device Manager (right-click on Computer (or My Computer), select Manage and then Device Manager).
3) Navigate to Ports (COM & LPT) and click on "cross" to show the ports.
4) Your cradle will show up us one of the COM ports. Mine was COM11.
5) Right-click on the port and select Properties
6) Click on Port Settings tab
7) Click on Advanced button
8) There's COM Port Number drop-down list. From that list select COM3 or COM4. Disregard "in use" message and warning.
9) Start PowerAgent software. Make sure that PowerTap is in cradle and turned on. PowerAgent shoud find the PowerTap on the new port.