ORA-01017 Invalid Username/Password when connecting to 11g database from 9i client

The user and password are DEFINITELY incorrect. Oracle 11g credentials are case sensitive.

Try ALTER SYSTEM SET SEC_CASE_SENSITIVE_LOGON = FALSE; and alter password.

http://oracle-base.com/articles/11g/case-sensitive-passwords-11gr1.php

for oracle version 12.2.x users cannot login using case insensitive passwords, even though SEC_CASE_SENSITIVE_LOGON = FALSE if PASSWORD_VERSIONS of user is not 10g.

following sql should show the PASSWORD_VERSIONS for a user.

select USERNAME,ACCOUNT_STATUS,PASSWORD_VERSIONS from dba_users;
USERNAME          ACCOUNT_STATUS    PASSWORD_VERSIONS 
---------------   --------------    -----------------
dummyuser         OPEN              11G 12C

to make PASSWORD_VERSIONS compatible with 10g

add/modify line in sqlnet.ora of database to have SQLNET.ALLOWED_LOGON_VERSION_SERVER=8 restart database change/expire password for existing user new users created will also have same settings after above steps PASSWORD_VERSIONS should be something like this

select USERNAME,ACCOUNT_STATUS,PASSWORD_VERSIONS from dba_users;
USERNAME          ACCOUNT_STATUS    PASSWORD_VERSIONS 
---------------   --------------    -----------------
dummyuser         OPEN              10G 11G 12C

I had a similar issue some time ago. You must be careful with quotes and double quotes. It's recommended to reset the user password, using a admin credentials.

ALTER USER user_name IDENTIFIED BY new_password;

But don't use double quotes in both parameters.