I had this problem with the desk top running XP 2nd but no problem with either of the two new laptops, that are the very top of the line Toshiba with Media Edition XP software.
This is what I had to do to make it work.


Here is the solution to the problem:

It seems to be a fault with Windows XP SP2.

You need to edit the registry. Navigate to the registry key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\Drivers32

If you look at the "midi 1-9" keys you will see that they are all taken up probably with the same driver. There seems to be a driver limit and Windows will not allow any more drivers even if all 10 drivers listed are the same driver! Delete one, exit the registry and uninstall then reinstall the Yamaha USB Driver and you will find you will be up and running.
This solved my problem and should also yours.
Bebop