Ubuntu 18.04 Hplip Scanner Problem

Problem

Printing works on Ubuntu 18.04 fine, but after a recent update, scanning on an HP MFP277 results in a SANE I/O Error 9.

Solution

Remove HPLIP:

$ sudo apt-get purge hplip

Download HP Public Key (Optional Step):

$ /usr/bin/gpg --keyserver pgp.mit.edu --recv-keys 0xA59047B9

Download HPLIP 19.x directly from HP, rather than from Ubuntu.

$ ./hplip-3.18.8.run

And select all the default responses.  Install plugins if requested:

$ hp-plugin

Checking for network connection...Downloading plug-in from: Plugin is not accessible. Trying to download it from fallback location: [https://developers.hp.com/sites/default/files/hplip-3.19.8-plugin.run]Receiving digital keys: /usr/bin/gpg --homedir /home/steve/.hplip/.gnupg --no-permission-warning --keyserver pgp.mit.edu --recv-keys 0x4ABA2F66DBD5A95894910E0673D770CDA59047B9

If the plugin is not accessible, as shown in the above example, simply download and execute the proposed plugin run file.

$ wget https://developers.hp.com/sites/default/files/hplip-3.19.8-plugin.run$ sh ./hplip-3.19.8-plugin.run

If the plugin install fails with the following error:

Plugin installation failederror: Python gobject/dbus may be not installederror: Plug-in install failed.

Ensure that a reboot following a previous upgrade is not pending.