Warning msg : Cannot start routing inside a keepout area or board outline

5.1.2 has a bug with cirlce or arc edge outlines. Move those edge cuts to another layer temporarily, move them back when you are done routing.
Or you can update to 5.1.3 release candidate https://kicad-downloads.s3.cern.ch/index.html?prefix=windows/testing/5.1/

4 Likes