"E: Unable to locate package mtp-tools", although universe repository is enabled. "AppStream cache update failed"

Question

I downloaded Ubuntu 16.04.3 LTS and installed the iso file as a virtual machine in VirtualBox running on Windows 7.

I enabled the universe repository:

sudo add-apt-repository universe

I got this result:

'universe' distribution component enabled for all sources

I updated:

sudo apt-get update

I got this result:

AppStream cache update failed

I then tried to download a package:

sudo apt-get install mtp-tools

I got this result:

E:  Unable to locate package mtp-tools