File Burning Issue

regularly record audio files using a Zen stone. The files record inWAV
format. In the past I simply open Roxio Creator 9, then use the path
Audio/Audio for Car or CD player/Add Music/navigate to the WAV file/select
and burn. But now I get an error message. If I try to add just ONE file, the
error message is:

"This is not a valid or supported music file. The following file formats are
supported: mp3, wma, wav, etc."

When I add multiple WAV files at once I get a similar error message:

"The following files could not be added to the project. And in a lower
window there is a similar message about the file format not being supported."

What is curious is that if I save these files to my computer and click on
them they play in Windows Media just fine. I simply cannot burn them to a CD.
I did copy them to a flash drive and try to burn them on another machine with
Roxio, but I get the same error message. This is an indication that it is
not an issue with the Roxio software (which I reinstalled to be sure) but
with the files themselves.

Here's another hint. I tried to burn old WAV files that I had SUCCESSFULLY
burned to CD in the past, but when I try to burn them now I get the same
error message as in the initial post. Those files were stored on my hard
drive, so they were not being corrupted by the Zen stone.

Ideas?

William