PL/SQL Developer Initialization error Could not load ... oci.dll

If the OCI file is not configured for PL/SQL Developer, then configure it.

If the configuration is okay, but PL/SQL Developer cannot be loaded (usually encountered in a new environment), it is not that the oci.dll file is faulty, but the dynamic library included in the Microsoft Visual C++ Redistributable Packages is missing.

To check, download the SQL*PLUS toolkit together with Oracle Instant Client and run sqlplus.exe. If it fails, the MSVCR120.dll not found error pops up. Install the corresponding version of Microsoft Visual C++ Redistributable Packages.