Samsung SPH-A800 / MM-A800

This is driving me crazy. I was able to copy MP3 files no problem over to the included 32 meg Transflash card included with the phone. I bought I 512mg transflash, and when I try to copy MP3s onto it, it says Error - The Device is not ready. I have exchanged three of the cards now, all the same result. No settings have changed on my computer, because I can still copy onto the 32 meg card. What is going on here, and what can I do? Any help would be appreciated