I am trying to compile / install the latest hplip with Mepis 8.

I went back to Step 2, Part C (http://hplipopensource.com/hplip-web...ros/mepis.html)

After installing the dependencies, I got lots of output in the terminal but it ended with this message:

WARNING: The following packages cannot be authenticated!
libdbus-1-3 libdbus-1-dev
E: There are problems and -y was used without --force-yes

Should I be concerned?

Ehh...that link should be:

http://hplipopensource.com/hplip-web...ros/mepis.html

Now it should work.

Get the GPG repo keys from the repo if you didn't already, or try an alternate mirror if there's mirror errors, or set "AllowUnauthenticated" to "0" in your /etc/apt/apt.conf to allow unauthenticated packages through (bad) or use "--force-yes" (bad) as Apt itself gave you that clue. As you see the problem with just saying "lots of output in the terminal" (instead of attaching a log) is that nobody can see what's going on (like NO_PUBKEY or repo errors) and have to list all possibilities. Not that efficient.

Point taken, here is the terminal input:

cat2007@mepis1:~$ su -c "apt-get install --yes libcupsys2 libcupsys2-dev libcupsys2-dev build-essential gs-esp openssl libjpeg62-dev libsnmp9-dev build-essential libtool libusb-dev build-essential python-imaging python-qt4 python-qt4-dbus python-dbus libdbus-1-dev python-gobject python-dev python python python-reportlab sane libsane-dev libsane-dev sane-utils xsane"

Point taken, here is the terminal output (concerned part is in bold):

Reading package lists... Done
Building dependency tree
Reading state information... Done
gs-esp is already the newest version.
openssl is already the newest version.
libjpeg62-dev is already the newest version.
Note, selecting libsnmp-dev instead of libsnmp9-dev
libsnmp-dev is already the newest version.
python-imaging is already the newest version.
python-qt4 is already the newest version.
python-qt4 set to manually installed.
python-dbus is already the newest version.
python is already the newest version.
python is already the newest version.
python-reportlab is already the newest version.
python-reportlab set to manually installed.
sane is already the newest version.
sane-utils is already the newest version.
The following packages were automatically installed and are no longer required:
libpng12-dev
Use 'apt-get autoremove' to remove them.
The following extra packages will be installed:
autotools-dev dpkg-dev g++ g++-4.3 libavahi-client-dev libavahi-common-dev
libdbus-1-3 libexif-dev libgphoto2-2-dev libieee1284-3-dev
libsane-extras-dev libstdc++6-4.3-dev python2.5-dev xsane-common
Suggested packages:
debian-keyring g++-multilib g++-4.3-multilib gcc-4.3-doc libstdc++6-4.3-dbg
libstdc++6-4.3-doc autoconf automaken gcj libtool-doc python-gobject-dbg
gimp hylafax-client mgetty-fax gv gocr
Recommended packages:
libltdl3-dev
The following NEW packages will be installed:
autotools-dev build-essential dpkg-dev g++ g++-4.3 libavahi-client-dev
libavahi-common-dev libcupsys2-dev libdbus-1-dev libexif-dev
libgphoto2-2-dev libieee1284-3-dev libsane-dev libsane-extras-dev
libstdc++6-4.3-dev libtool libusb-dev python-dev python-qt4-dbus
python2.5-dev xsane xsane-common
The following packages will be upgraded:
libcupsys2 libdbus-1-3 python-gobject
3 upgraded, 22 newly installed, 0 to remove and 110 not upgraded.
Need to get 16.8MB of archives.
After this operation, 53.2MB of additional disk space will be used.
WARNING: The following packages cannot be authenticated!
libdbus-1-3 libdbus-1-dev
E: There are problems and -y was used without --force-yes
cat2007@mepis1:~$

OK. thanks for posting. Temporarily set "AllowUnauthenticated" to "0" in apt.conf or use apt with "--force-yes"?

IIRC, Mepis 8 comes with hplip installed....or at least it's in the repos...