Now trying brian_p's change... I noticed there are two entries labeled "[hp_laserjet_mfp_m28-m31]" in /usr/share/hplip/data/models/models.dat ... I changed both to [laserjet_mfp_m28-m31]...
And could not scan again... I had to re-add the printer using Gnome's Control Center.
Then the same error happens again error: SANE: Error during device I/O (code=9)
I'll add a dump of /var/log/syslog with the next message
Now trying brian_p's change... I noticed there are two entries labeled "[hp_laserjet_ mfp_m28- m31]" in /usr/share/ hplip/data/ models/ models. dat ... I changed both to [laserjet_ mfp_m28- m31]...
And could not scan again... I had to re-add the printer using Gnome's Control Center.
Then the same error happens again error: SANE: Error during device I/O (code=9)
I'll add a dump of /var/log/syslog with the next message