I have the same problem.
Spec:
Nds Lite supercard, flashed bios, sandisk 1gb microSD. Soft V2.56 supercard for micro sd pro version.
I think that the software that is the problem, but I dont know what I should have instead.
btw i feel this a good time to remind you guys that sea of thieves was made by rare, who also made DKC1-3 and DK64, alongside banjo kazooie and conker's bad fur day