Your application is receiving other than ojdbc5.jar (probably 4) when the app is receiving it and it's probably there in classpath somewhere.
Use startServer.log to findout your classpath entries and remove it from there.
Not that if it's there in application classpath dir, ex, web-inf\lib, system won't show that entry in startServer.log.
Two other possible causes:
1. Data source custom property oracle9iLogTraceLevel must be blank
2. WebSphere AS service pack level must include IBM's fix for problem of using 9i methods against 10g/11g database
subject: Exception while strting Websphere Server with Oracle 11g