An ORA-12710 error occurs when SQL*Net cannot connect to its
destination. Common causes are firewalls blocking connections and
network routing errors.
Open firewall settings and ensure the listener port is not blocked.
For example, on a Windows system, navigate to
Control Panel-> Security Center-> Windows Firewall-> Exceptions.
Click on Add port and add port 1521 or whatever port the listener is
running on (see listener.ora).
