Hi Ivan…
I was just reading through posts and saw the followup on @geek2nurse’s post with the same problem; A little bug?
This very thing just happened to me, again…got my files moved around and they all froze up so they were immovable. I clicked a different PG material in the left hand column, then clicked back to my correct chosen material and I was then able to move my files. Like Ruth, I’m 99% sure this problem has something to do with the set focus, too…but I don’t know in what way. Just wanted to update you. Thanks…