Error received when connecting to database:
"ORA-12560: TNS: error adapter protocol."
Connecting via Command Prompt | sqlplus also gives the same error
Firewall may be preventing connection to database.
OR
IP address of the database server not added to hosts file.
RESOLUTION 1:
Make sure that you have a database selected in the database field on the connection screen.
RESOLUTION 2:
If a firewall is enabled, try turning it off and then connecting.
RESOLUTION 3:
Add the IP address of the database server to the Hosts file in C:\WINDOWS\system32\drivers\etc folder.
RESOLUTION 4:
Go to your Environment Variables, and add a 'new' System Variable named, TNS_ADMIN, and point the Value to the location path of your tnsnames.ora file i.e. C:\oracle\product\10.2.0\client_1\NETWORK\ADMIN.
RESOLUTION 5:
Reboot PC to update all setting may fix the issue.
RESOLUTION 6:
For Oracle Instant Client setup, the Oracle Instant Client path in the Environment Variables, PATH, is not in the very beginning of the PATH. Please adjust this. The TNS_ADMIN also contains the wrong path to the tnsnames.ora file. Please adjust this as well.
