Hello,
I’m having trouble running any Intellivision title. I figured out I had to rename the roms filder to intv but I’m still clueless about the BIOS files.
I added grom.bin and exec.bin to /roms/intv/ as well as on /system/ and /system/mess/ but I keep getting the attached error message.
I also downloaded ro-3-9503-003.u21 and copied to all the aforementioned folders and it acts as if it’s not there.
Any help? 
Edit: figured out sooner than expected, I just had to create folders with the needed BIOS images (uncompressed) within the /roms/intv/ folder.