The only two I can recall are tyrano/images/system/arrow_up and arrow_down, not sure if they are png's or jpg's. Those are the up/down arrows for the scrollbar in the history view. There were others, but I couldn't figure out how to replicate them.
Even though I don't have the up/down arrow image files, the scrollbar now has up/down arrows, which it didn't before. Whatever caused the error, it's not happening anymore. It is possible that Tyrano was looking for OS assets and could not find them, and so looked for backups. I did have a Windows update and reboot in between the last time I played the broken version and when I reinstalled a working version, so the problem could well have been with my system and not the game.