ORA-01920 user name SAPR3 conflicts

I am stuck at sapinst phase CREATE DATABASE SCHEMA where sapinst is running a script named oradbusr.sql and getting following errors.

I am creating a new Training box by using database copy method from Production. Oracle DBA team has imported the database and DB is up and running when I started sapinst.

Platform = AIX/Oracle 10.2.0.2

Sapinst: ERP 2005 SR2.

Source : Production: SID=SA3, DBSID=SA3 and SCHEMA=SAPR3

Target : Training box: SID=TR2, DBSID=TR2 and SCHEMA=SAPR3

So we want to only change the SID not the Schema ID.

The last error that I am getting are these in the SAPINST running directory:

ERROR at line 1:

ORA-28007: the password cannot be reused

ORA-06512: at "SYS.DBMS_SYS_SQL", line 906

ORA-06512: at "SYS.DBMS_SQL", line 39

ORA-06512: at line 102

ORA-01920: user name SAPR3 conflicts with another user or role name