I just had a go at this using the latest updated 1.7.0 dev build and it is being extremely weird and finicky. It does "sort of work" but you have to remove the old command line parameters --nogui --fullscreen --fullboot if you have them and it seems to only work with some games and not others even though those games do work when launching them via command line using a Windows DOS prompt. I cannot find a pattern for why some games will load through Launchbox while others don't. The file extension doesn't seem to matter, neither does the folder structure.