I am also getting the same error on my end:
RetroArch [INFO] :: null: [sdmc:/retroarch/content_history lpl].
RetroArch:: cannot push NULL or empty core info into the playlist.
Along with another issue that isn't so much an error but an alert that I have noticed as well:
RetroArch [INFO] :: Environ SAVE_DIRECTORY: "ssmc:/retroarch/cores/savefiles".
config_path is : sdmc:/Roms/gba/game_config.txt
game config missing
Despite having those two messages come up on my bottom screen, I am still able to boot gpSP v0.91 and play Minish Cap as well on my setup..
It may possibly be something on your end though because I am not booting the .cia I am booting the .3dsx since I am booting through Homebrew.
Check your BIOS I did an internet search for GBA Bios and came across one on the internet. It may possibly be the BIOS and/or Rom.
update:
Check the ROM because if other GBA Roms are running fine with your current BIOS. It may have possibly been a bad dump or the ROM itself may be corrupt somehow.
I think the freezing issue may have something to do with the Kernel hack. I just recently used the 3dsx versions on the most recent release and it works, while the 3ds and cia ones don't.