Oracle has two methods of signon …
1) users and passwrods defined to the Oracle database as in CREATE USER username IDENTIFIED BY pass_word
2) users that Oracle will allow to be authenticated by the operating system as in CREATE USER username IDENTIFIED EXTERNAL
the second ones (used to) default to prefixing the userid with ‘OPS$’
you state “login to the application”. Well, at that exact moment, you really aren’t connecting to Oracle, you are executing a program. Is the program connecting to Oracle? Is that the exact moment you are getting the error? Then your app needs to do one of several things; connect to oracle passing the uid & pw that came into the program , connect with its own username (which needs to be defined to Oracle) , depending on the platform, you may have to have the program prompt the user for the Orcle username and password.