it's also buggy in Ubuntu Ubuntu 16.04.5 LTS. I solve with remove or modifying name of grub-pc.postinst to grub-pc.postinst.buggy. But sometimes if you update your ubuntu, the grub-pc.postinst is back to /var/lib/dpkg/info, and you're getting same error.
it's also buggy in Ubuntu Ubuntu 16.04.5 LTS. I solve with remove or modifying name of grub-pc.postinst to grub-pc. postinst. buggy. But sometimes if you update your ubuntu, the grub-pc.postinst is back to /var/lib/dpkg/info, and you're getting same error.