I have a Nokia 822 with expandable micro SD card. Specs say 64 gb is possible, I use a 32 gb. After weeks of frustrations with music I think I have something working now. I've chatted with Nokia's site, no luck - didn't get anyone who had a real answer.
Everytime I put an mp3 or wma file on the phone from my own PC collection, the file would 50% of time time be unreadable with error 80070002 or 80070003 or other errors. The card would become corrupt and I would reformat it on my PC. I tried FAT32, exFAT both with the same result. I would only use the Windows Phone desktop app for Win7 to move the files and would get the errors. If I stored the music on the phone's internal memory it seemed to work better (at least the corruption would stop) but again 50% of the files where not playable.
I tried to transcode all my music to .wma as this format seemed more friendly, I was wrong same problems. So I did the hard this and hard reset the phone and re-formatted the SD card and started fresh. Some music transferred with no errors, but then the playable problem persisted again with mp3 or wma.
I noticed that WP8 supports AAC files, so I transcoded all my files to AAC (actually .m4a which is just another file extension but is AAC format inside). I use foobar2000 freeware to do the work.
Then I transferred the music using just windows explorer and low and behold the music is there are readable. You even get a windows pop-up saying that the device doesn't support .m4a files but I transferred them anyway and it's working perfectly. Hard to beleive mp3 and wma implementation on WP8 is so terrible, even my BlackBerry handeled this with ease. Love everything about the phone, I just don't like to have to transcode music to listen to it.