ORA-12557: TNS:protocol adapter not loadable

--  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.

Solution:  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

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

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

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

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