My demo file for students has had a Metal and a Metal3 option available for a couple of years. Seldom used, but previously with no issue.
In checking through the file after syncing to v1.7 of LBT today, I noted two red material definition files. Nothing has changed in the inputs but now they generate an error.
Said error disappears when I remove the diffuse reflectance entry
I think this is a code change?