Hi! The error means that the gbvm can't find your tileset file. Is the tileset saved in the file "tileset2.png"? If it is and you are still grtting errors then GB studio might have made another internal name for it. If so try making a GBVM script event, add reference, and find what the file is called internally. If it's something like "__bank_bg_tileset_2_tileset" than enter tileset_2 into the tilemap name.
For unique tiles you can change the tileset scene type to logo and all tiles will automatically become unique. Hope this helps!