Maybe your card is worn out. Try to completely erase, I mean all sectors with SD Formatter full format or with HDD Low Level Format Tool.
Then format again to FAT32, copy files, verify the integrity of the copied files with QickSFV or something like that.
Possible I just got the card when I got my X3 so it has not been more than a couple weeks. I just did a low level format , we will see.
The strange thing is I could see all of the albums if I used browse, but under album or artist everything is not seen. Updating media would freeze the unit and sorting the songs were in the incorrect order even in browse mode. Everything was fine a couple of days ago.