@Mii09, are you matching the game and its DLC with the same region? Look in
FBI → Titles list for these title IDs. For USA releases:
Etrian Odyssey 2 Untold: The Fafnir Knight
- 000400000015f200 - game
- 0004008c0015f200 - DLC
Etrian Odyssey V: Beyond the Myth
- 00040000001c5100 - game
- 0004008c001c5100 - DLC
Radiant Historia: Perfect Chronology
- 00040000001c8f00 - game
- 0004008c001c8f00 - DLC
***
Other than that, the only other thing I can think of is that you should check if your SD card is fake or faulty.
- Copy everything off the card onto a computer.
- Reformat it as FAT32 + 32 KB cluster with Windows File Explorer or guiformat.
- While it's empty, run a Full Write + Verify Test with H2testw.
- Delete the *.h2w test files if it passes.
- Stop the test if an error was report. Replace the non-fixable card, and go back to step 2 or 3.
If your card was reported with a continuous error stream, your card's fake. This would mean much or all of the data on it is corrupted.