ORA-38730: Invalid SCN/TIMESTAMP expression.
Cause : The expression supplied in a FLASHBACK DATABASE command was invalid.
Action - How to fix it : DBA Scripts :: www.high-oracle.com/scripts
Retry the command using a valid number or time stamp expression.
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.