\uD83E\uDD14 Problem
User is trying to install Biovia Direct 2021 on a database server with Red Hat 7.9 and Oracle 19.13. User have followed the Installation and Configuration Guide for Linux. User chose to use the more secure setup with a listener running as a non-privileged user (biovia, same as software owner). Issue is, after starting the listener and in section "Install the Direct Oracle Schema and Cartridge Objects", when running the script mdltestlistener.sql, user get: ORA-06520: PL/SQL: Error loading external library
\uD83C\uDF31 Solution
ORA-06520 error can have different and also multiple sources, please have a look at the following article that posted on the BIOVIA Community on specifics running the Direct listener from a non-privileged user account: https://r1132100503382-eu1-3dswym.3dexperience.3ds.com/#community:xFN-z9cuQ02uCml-D0wYww/post:37R_LATyR2SlZgP9ovYTAQ