I did find that support information. Thanks.

Checking the soundcard (Realtek High Definition Audio, using ASIO4All) under Options/Preferences/Audio and clicking on the "Default" button, I get similar error message about conflict for the soundcard using something else.

I'm wondering whether the "something else" is actually RealBand and that is why Windows Media Player can't play the demo Realtracks? Because if so, that's just nuts!