YSMenu might not like your microSD card settings.
Huh, YSMenu boots from the flashcart now, and it has a Pokemon Black/White theme that I didn't put on there. Booting a ROM in YSMenu from the flashcart itself gives me "Unsupported DLDI Name" while booting a forwarder brings me to the YSmenu ROM selector where booting a ROM works fine.Alright, I'll try that and a completely different SD card.