Compute milling paths
This article is part of a TARGET 3001! Crash Course Frontpanel.
After clicking the icon 
the following image shows::
Image 1: milling paths (green) are computed...
The green lines are created upon layer 32, Frontpanel milling. Have a look there to delete them if needed. Open menu View/Toolbars/Sidebar visible to fade in the sidebar where you can edit each layer.