Moving this topic from the GBA section.

I was given this SLOT-2 cart a few days ago, and it works great as a memory expansion pak and GBA games with GBAExploader. These functions work fine but I can't seem to boot the cart. Without the MiniSD inside, it tells me to insert the card in, and if I decide to continue without it, it hangs right after the non-Nintendo authorised item screen. When I plug my memory card in it instead shows me two blank screens.

A bit of searching says that the M3 is picky with memory cards, and Sandisk ones tend to work best. I'm using a MicroSD to MiniSD converter here as MiniSDs are getting quite rare, and I have tested all of my Sandisk MicroSDs (three of them, in fact) and none of them seems to work at all. Same case when I place the firmware update inside the cards, and formatting them to FAT32, changing cluster sizes, that sort.

Anyone with a solution for this?