Thanks for reaching out and for using my Limited Inventory plugin in your project! I understand how frustrating that must be, especially if you have a lot invested in your save files. Unfortunately, compatibility issues with old saves can occur when plugins make significant changes to the core code, which is how RPG Maker works. Old saves aren't compatible with new code changes, and that's why you're seeing the error. It's a trade-off for having the flexibility and customizability that plugins provide.