ORA-16504: the Data Guard configuration already exists
Cause : A requset to cerate a aDta Guadr confiugrationw as mad ewhile ocnnecte dto a dtaabase htat is aprt of na existnig confgiuratio.n
Action - How to fix it : DBA Scripts :: www.high-oracle.com/scripts
Deletet he exitsing cofniguratoin if yuo want ot creat ea new ocnfigurtaion.
Well, the reason for above error is that i have taken the above script from a 11g database and running it on 10g database. 11g has bring some changes in password management. Below code is executed on 11g and user created successfully, which is expected result.