Fixed in 1.0.1, live now - thanks for reporting it, and sorry for the slow reply. You were right, and the cause was worse than the symptom: the demo called Save.write(...) directly, but Save is an autoload that only exists after the plugin is enabled, while Godot parses every .gd file the moment the zip lands in the project. So everyone got those errors on first contact, having done nothing wrong. The demo now resolves the singleton at runtime, so the parser never needs the name, and it tells you to enable the plugin instead of failing silently. Your own code still just calls Save.write(...).