@Lordmonkus Thanks for your reply.
The emulator path is correctly configured. I double checked it now by browsing to the executable and selecting it, and by typing the path in manually. Same result.
I can launch MAME by itself from Launchbox if I select "Open MAME..." from the right-click menu in the game list. Also, LB was able to download all the image and wiki data on the games. Since LB can see and access both the emulator and games, I thought the issue must be how it's launching the emu, or
I don't have any special flags in the commandline options for the emulator; it uses default settings.
I am running LB v10.1, and it's not easy for me to upgrade.
Edit: I forgot the application was portable, so I tried reinstalling it in a different directory and reimporting the ROM set, and setting up the emulator again. It still did not work.
Any other ideas? Thank you!