You can try to:
- Uninstall the extension first from Edit > Preferences > Extensions, it might throw this error, ignore it
- Close and reopen Aseprite, make sure it’s removed in Prefer Edit > Preferences > Extensions
- Try installing Magic Pencil fresh, v1.0.3 would be the best, this shouldn’t throw an error
- Restart Aseprite and check does Magic Pencil appear in the Edit menu and does it work
If this doesn’t help, please provide:
- Aseprite version
- Operating system version I’ll try to investigate this issue further.