You shouldn't ever get an error message. The only time I ever got an error message was when the cable fell out during a file transfer and I ending up having to reformat the card *and* the X3 to get rid of the resulting problems. What error do you get?
When you say that you can't see the files on the X3, do you mean that you can't see them in categories, or that you can't see them using the file browser, or both?
If you can't see them in categories, have you tagged them?
Yes, I'm pretty obsessive about my music library - ID tags, album cover art, etc. The error message I'm getting is that when eject the SD card and then the X3 (or vice versa), it reads "the device has not been ejected properly" or something to that effect, when in all actuality, it has been. Still, that shouldn't affect the ability for the card to be read by the x3 when I'm in the artist or album category. But it's happening nonetheless.
I placed an email to Fiio tech and awaiting their response. In the meantime, Agent XXl was also kind enough to post something regarding formatting which I'll take a look at. Thanks, all. I'll keep you posted...