I started getting this error when I tried to create a footprint library after downloading a footprint from SnapEDA. I also get this error for a footprint library from DigiKey (after wading thru their 10 episodes of learning to use KiCAD).
Using KiCAD 5.0.1-4 and Win10 Pro on a home network.
I’ve noticed all my folders seem to be “Read Only” but files aren’t. I suspect they’ve all been that way for some time as I see the same thing on another computer.