There have been many threads about the "boss" crash. It is very mysterious.
Copy everything off your SD card (Roadkil's Unstoppable Copier is recommended since there's a possibility of corruption), format the card, test the empty card with h2testw, and copy everything back again. See if that fixes it. If the test fails or if you can't format the card, then you should get a new card (and copy everything to the new card after formatting and testing it).
Otherwise, doing an update in Safe Mode sometimes reportedly helps.
suggests doing a CTRTransfer, but you should probably try those other things first.
Are you using Netpass?
Also, that's a very annoying thing to say. Are we just supposed to guess about what you've done and suggest things you've already tried..?