Werner,
I didn't look into this yet, but this slipped to my mind :
I think because of the phenomenon "jack sensing" I discovered (already many months ago) that if you'd switch off the power amps (or one of them), this might influence the DAC, and because it talks to the software (in Vista), the software is triggered to shut off (like it won't run with the DAC out of power -> try it). BUT : where I should capture such a situation, I completely forgot about it. Now :
Suppose ... just suppose your DAC, by whatever means, responses to an end of track situation the wrong way (or the MS Class USB drivers you'd be using don't respond to that appropriately) ... it would be a perfect reason for the player to respond back with a "does not work anymore" (translation from dutch from what you described).
It's a bit of a long shot, and I wouldn't know how you could deal with this in discovering whether this can be the culprit.
What *I* can do, is trap this situation, and if from then on you'd get "my" error message, it should be in the direction.
Currently I've some other priorities though, but I sure won't forget it !
Thanks for your patience.
Peter