Hi-
There was a little bit of bad formatting in the previous post, as the URL got converted into a link, so directly copy/pasteing wouldn't work...
Just to make sure that this isn't the issue, could we retry Step #1 again, with copy/pasting *this line*:
deb
http://security.ubuntu.com/ubuntu/ precise-security main
... into "/etc/apt/sources.list" (again, probably you need to type "sudo" in the command to open it up in an editor), and then run these:
sudo apt update
sudo apt install libxp6
... and see what that does for your afni_system_check.py, and/or checking the aptitude install list with:
apt list --installed | grep libxp6
Thanks,
pt