Some 1G cards definitely work with the Panasonic Jukebox software and card reader. I have successfully used Sandisk and TPro cards. There was another brand of 1G card that my friend tried with similar problems to yours (I can't remember the brand).
I also encountered similar problems with a 256M card from PQI whilst a 512M card from the same manufacturer worked perfectly. It would appear that there is a variation in card specifications even from the same manufacturer.

Cheers
Len C.