RPi3 and RecalBox 4.0.

When I try to install Game Gear Roms (extension .GG) through the browser, they all fail with the message "Your file does not seem to be a valid Rom for this system."

I can get some of the games to work by changing them to .sms and installing them in the Sega Master System, but I'm not happy with that solution at all.

Has anyone else had this problem? How can I solve this problem?