[PyQt] Phonon VideoWidget error: "the video widget could not be initialized correctly"

[Daniel Naab]

I've encountered a frustrating issue (on Windows only): when trying to  
create a VideoWidget instance, I'm getting the error message "the  
video widget could not be initialized correctly".  Oddly, this just  
surfaced in the code after several weeks of perfect operation, on two  
separate Windows boxes (one Vista, the other an XP image running via  
Parallels).  I'm not aware of anything having changed in the  
environment that may have caused it.

I'm using Python 2.6 and the PyQt 4.5.4 Windows installer.  I notice  
this issue was raised last November, but no solutions were offered:

http://www.riverbankcomputing.com/pipermail/pyqt/2008-November/021029.html

My Googling hasn't turned up any explanations of what may cause this.   
Can anyone clue me in?

Thank you.