Hi!
It seems to be the LibFredo6 because (apart from basic SketchUp extensions) I only installed Fredo6 extensions and the bug occurs.
However, sometimes it resolves itself and the Toposhaper toolbar appears.
I haven't been able to find a routine that produces the bug for sure.
After installing Curviloft (same message as after installing FredoTools)
-.-.-.-.-.-.-
Since installing version 13.5a, the bug no longer seems to occur but
there are always error messages for installations of extensions requiring a Fredo6 license.
After install of FredoSpline:
Thanks a lot for your speed react