Try uninstalling FredoLibrary, then download and reinstall it, followed by updating Curviloft. This often resolves hidden dependency conflicts.
3.5. Rule-based constraints (RBZ) Formulate rules as: curviloft rbz
At its heart, Curviloft is a tool. While native SketchUp excels at pushing and pulling flat faces, it struggles with the mathematical complexity required to generate a skin between two different shapes or along a curved path. Curviloft solves this "how do I fill this gap" problem by automatically creating high-quality, quad-based meshes from user-defined skeletal lines. Try uninstalling FredoLibrary
The plugin consists of three primary tools, each suited for a different modeling scenario: then download and reinstall it