Running on Mac, I was trying to run by opening up "mkxp-z" to run the game. However, the game kept crashing when pidgey tried to evolve, so I came to this forum and read that I should not run the -z file.
I figured out permissions so that I can run the application just by clicking on the main icon, but now when I try to play from my save file, the attached error pops up.
I checked that the LastSave.dat file has read/write permissions from everyone, so not sure what the issue is. I'm also not sure where the saved game backups are stored.
EDIT: I've been running on the -z file, and it still crashes not just when Pidgey evolves, but also when I've tried to evolve my zigzagoon. Other people like froakie have evolved just fine though.
Thanks in advance!