ORA-12557: TNS:protocol adapter not loadable

Question:  What causes the ORA-12577 error below?  I am running on Windows.

ORA-12557: TNS:protocol adapter not loadable

The ORA-12577 error is related to Windows Environment or Oracle Home PATH because sqlplus command works smoothly when I execute it inside ORACLE_HOME\bin.

Answer:  There are two solutions to this issue:

1 - put the Oracle DB Home in front of the other paths in the PATH environment variable.

2 - Remove ORACLE_HOME From environment Variable and re-boot PC

Oracle author Osama Mustafa notes a solution to the ORA-12577 error.

RUN: SYSDM.CPL to open Windows System Properties

Click on Advanced Tab > Environment Variables…

Click the Path variable under System Variable, then click Edit…

Change the order between Oracle Client Home and Oracle DB Home:

From: D:\oracle\product\10.2.0\client_1\bin;D:\oracle\product\10.2.0\db_1\bin;

To: D:\oracle\product\10.2.0\db_1\bin;D:\oracle\product\10.2.0\client_1\bin;

In other words, put the Oracle DB Home in front of the other path.