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

I'm trying to connect to a schema on 11g (v11.2.0.1.0) from a PC with 9i (v9.2.0.1) client. It seems to connect fine to some schemas, but not this one - it comes back with a ORA-01017 Invalid Username/Password error every time.

The username and password are DEFINITELY correct - can anyone think of a reason why this wouldn't work?

Are there any fundamental incompatibilities between 9i and 11g?

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.

If all else fails, try resetting the password to the same thing. I encountered this error and was unable to work around it, but simply resetting the password to the same value resolved the problem.