Had the same issue I believe, as I also just did a apt-get upgrade, seem to remember it was a perl compilation error in pve-daemon due to a missing new libhttp*perl* package which didn't get added before I did apt-get dist-upgrade...
Thanks for posting your solution, this helped me. After runninghi i have remount with
mount -o remount,rw /
after it works, but why it was read-only mounted?
mount -o remount,rw /
everything worked