Oracle 11g now sets the password case sensitivity setting to TRUE by default. If you are running any application that connects to an earlier version of an Oracle database, chances are you are sending the connect string in all caps within the application (ex: USER/USER@ORCL11G when it really should be user/user@orcl11g). Make sure you are aware of this when developing your app and if the case is that you want to have case sensitive passwords, use double quotes to enclose the password string (ex: USER/”user”@ORCL11G). To disable password case sensitivity, just change the value of the system parameter sec_case_sensitive_logon:
alter system set sec_case_sensitive_logon = FALSE;
FALSE disables password case sensitivity and TRUE enables it.