RESOLUTION #1:
Change existing firewall or antivirus setting to allow Toad.exe as an application to connect to database.
RESOLUTION #2:
If using direct connect, make sure that the correct information is entered. You may need to use the IP address for the server name.
RESOLUTION #3:
If your company is using LDAP, ensure you also copy over the LDAP and SQLNET.ora files to you Oracle Client Home (Network\Admin folder) location.
RESOLUTION #4:
If you use Oracle Full Client check if the client is installed correctly. Try to start SQLPlus. You must be able to connect to the database using SQLPlus.
RESOLUTION #5:
If you use VPN to connect to your Oracle DB, please ensure your VPN is connected.
