I have installed oracle 9i and iam unable to open sqlplus with scott and tiger. I tried many other usernames and passwords like system/manager, sys/sys as sysdba, sys/change_on_install but iam unable to login sqlplus. With scott/tiger, it is giving TNS protocal adapter error and with sys/sys as sysdba, it is showing invalid username and password. I need help. Reply me as soon as possible.