Open a terminal and type:
$ sudo cp /usr/lib64/sane/libsane-hpaio* /usrlib/sane
and I have seen this solution before as a suggested solution on the hp launchpad bug reports, but if you look at a fresh install, there is no /usr/lib64, so I think this is a deprecated solution from before the move to a multiarch specification (https://wiki.ubuntu.com/MultiarchSpec)
And for future reference, I note in the syslog
Dec 24 08:49:38 4530s simple-scan: io/hpmud/jd.c 790: error mdns lookup HPC68655.local: bad hostname in reply from ip=192.168.1.122 port=5353
even though the device was on 192.168.1.104, which was what was reported by hplip (even added manually at that ip).