I had a similar situation to others in that my WD My Book external drive all of a sudden became partially write-protected. I don’t seem to be able to post to the forum on the topic, but want to share my solution. I noticed that there was a rectangular button just above the plug-in for the USB cord, so I pushed it several times, and then disconnected the power plug from the drive. I waited a short time, and plugged it back in, and after re-opening it with my password, I discovered that I could navigate to all the files that were previously write-protected and were now no longer write-protected.
I’m not sure which action cleared the unit, but now it is fine. I did have several small things sitting on top of it so it could have also been a heat issue as others put forward.