Years ago (exactly how long ago in a minute) I recorded a short WAV file that I used as an announcement that my daughter had gotten on AIM.
When I upgraded to Windows 7 I set this as a pidgin Buddy Pounce. But it didn't work!
Oddly Windows Media Player would play it but Media Player Classic wouldn't nor would Windows 7 play it as a system sound. Hmmm.
Off to Google.
It wasn't on the first page but on the second page was this link.
That held the key and the solution to the problem.
I had recorded that WAV file using Windows 98's Sound Recorder application.
I fired up AudacityPortable and opened the old WAV file. Then I exported it as a WAV but obviously Audacity used a different codec.
That fixed it.