I have quite a similar problem. At first run, the same error message appears. Then after running again, the generation dialog appears for a split second and diappears without doing nor showing anything. It used to work fine before but now I cannot use it. I have tried putting contours without materials in a brand new group all in the Untagged tag but it doesn't work.
Sketchup 2021. All plugins and libraries updated. Usage under bundle purchase.
Please help.