ORA-28270: Malformed user nickname for password authenticated global user.
Cause : An attempt to login as password-auuthenticated global user with a malformed user nickname.
Action - How to fix it : DBA Scripts :: www.high-oracle.com/scripts
Make sure the nickname is valid and re-login.
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.