I’ve experienced this type of error too. The usual fixes include, intersecting geometry or redrawing the shape in question.
Intersecting geometry would probably be better for your situation. Can you help us recreate that error? Do you know a certain chain of commands that will always create that error?
The root of the problem is much of the model is slightly noncoplanar.
While it is possible to fix such things, starting over is generally faster and easier.
Learn to use Inference Locking to avoid the problem. Inference Locking — SketchUp Help
