Disabling sophos antivitus has fixed the problem for me. See original comment at https://bugs.launchpad.net/ubuntu/+source/dpkg/+bug/1739991/comments/3
Disabling sophos antivitus has fixed the problem for me. See original comment at https:/ /bugs.launchpad .net/ubuntu/ +source/ dpkg/+bug/ 1739991/ comments/ 3