Do you have created the MARCADS directory in the root directory of the M3 and put MarcaDS.nds in it , with the roms in ZIP format with NO COMPRESSION ?
Yep, done that. I have three files in the MARCADS directory: MarcaDS.nds, bombjack.zip & mario.zip.
I downloaded the games and unzipped the files, checked that all the files are there compared to gamelist.txt and then I right clicked the files and choosed "Add to archive.." and added the files in WinRAR to a zip-format archive with compression method "Store" (=no compression).
The SD-card is formatted with FAT-32 and I have labelled it.