The fix you're mentioning works on some distributions, but not on all. Some distributions use the /etc/ld.so.conf.d/ directory, in which the ARGoS installer puts a dedicated file automatically.
Other distributions don't use this directory (but they're becoming rare, because it's the old system), and require you to edit /etc/ld.so.conf as you correctly posted. In this case, you get the above error.
Moral of the story: always specify the type of distribution you're using
Final word: thanks for linking the article and taking the time to share!
![Smile :-)](./images/smilies/icon_e_smile.gif)
I made ARGoS.