Hi!
Unless you are running a very old version, amportal is deprecated and has been replaced by fwconsole..
Every call to amportal is actually forwarded to fwconsole…
Also, is it under /usr/sbin/amportal or /usr/local/sbin/amportal on your system? You mention that /usr/sbin/amportal is missing but then you copy /usr/local/sbin/amportal to /var/lib/asterisk/bin/amportal (my guess is that you wanted the exact reverse of what you did…).
I believe you followed the suggestion given in the link in that post
which was not the right fix…
Also,/usr/sbin/amportal, at least on FreePBX 14 distro but most likely at least a few earlier versions as well, is a symbolic link to /var/lib/asterisk/bin/amportal not the other way around and you don’t want to copy it but actually do a symbolic link to it.
re:
ln -s /var/lib/asterisk/bin/amportal /usr/sbin/amportal
(I assumed here /usr/sbin/ is the right path…)
Could you please give more info about what you are running, which FreePBX version and which Linux distro you are running? Missing files makes me think that rounded down it has something to do with 3… 
Good luck and have a nice day!
Nick