This error occurs due to the fact that your connection to the Oracle server is no longer available or that the server couldn’t respond to the client’s requests. This is usually called by an Oracle server issue or a networking issue.
You can start troubleshooting by making sure that your Oracle server, Oracle Database, and Listener is up and running. If everything is up and without errors, then try another client box or at least make sure that the error is happening for everyone.
If you’re still at a loss you can check the logs in the user_dump_dest that should help you find the root cause of the problem or at least assist your DBA in helping you troubleshoot the issue. It will also help your DBA to narrow down if this error occurs when trying to make a connection or with an established connection.