Error installing or upgrading flashplugin-installer
Can’t drop privileges for downloading as file ‘/var/lib/update-notifier/package-data -downloads/partial’
Start up synaptic and install flashplugin-installer. Error will not appear. There is a difference in apt-get install flashplugin-installer and synaptic, that apt-get does not run with full privileges, whereas for synaptic to install packages you are asked to enter your password to run synaptic as sudo.