Cause sounds like either a defective cartridge, or perhaps the update was corrupted. Delete any extra data, re-install the update, and if that doesn't work, try the eShop's Download Software Repair Tool on the update.
What to Do:
- On the HOME menu, select the Nintendo eShop icon.
- Once the Nintendo eShop loads, select the "Menu" icon from the top-left of the touch screen, and then scroll down through the list and select "Settings / Other."
- Under the "History" section, select "Redownloadable Software."
- Select "Your Downloads," located in the bottom right corner.
- Scroll through the list of titles to find the software you'd like to check for repair, and then click "Software Info."
- Scroll down to the bottom of the page and tap "Repair Software," and then tap "OK."
- This process will check the download data for errors. If no errors are found, you can still choose to repair the data.
- The time it takes to check for errors will vary depending on the size of the software being checked.
- You will receive a prompt stating the software check was complete. Tap "OK," followed by "Download" to initiate the repair process.
- The repair process will download the software again without overwriting the software's save data.
- Download time will vary depending on the software being repaired.
- When finished, click "Continue" to return to the software info page.
- To return to the HOME Menu, press the HOME Button.
If that doesn't work, your best bet would be to call Nintendo's support line at 1 (800) 255-3700.
Best of luck to you~