Getting error ORA-12557 on Windows environment with multiple installations

Symptoms: Your Windows environment has more than one ORACLE_HOME and it is presenting error such as ORA-12557 TNS:protocol adapter not loadable.

Cause: The error happens on Windows environment and it has to do with PATH and ORACLE_HOME variable.

Solution: You can unset the ORACLE_HOME (better remove the variable instead of just unset via command prompt) or you can change the order of values on PATH variable, putting the ORACLE_HOME\bin at the end of the string. Reboot the machine and try again to connect on the database.