Most of the software firewall are designed to provide you a kind of moderate level of security from unwanted intrusions, however at certain occasions, this could jeopardise certain legitimate connection requests…including Quest Toad TNS connections.
Prior breaking your head against the walls, give it another try by disabling the firewall if you receive the error “ORA-12546 TNS:permission denied”, and all other client side oracle tools successfully connect to Oracle database without any issues.
If the firewall was blocking the connections, create exceptions for Toad.exe and enjoy.

Regards,
Admin