@garsdaledesign,
Thanks for the reply.
I think it's a memory bug too. Badly, when this issue has happened I saved the scene, so even I restart CityEngine the error is still there. Fortunately, I do a backup of the file, I didn't lost all my works...
@matthiasbuehler
I can't reproduce the issue again from a new scene. But I remember it happened when I drag a rule to a shape. By the way, the file will save the error into it? Cause I saved the file, when I reopen it the issue is still exist.