Hi Rajesh,
a wired issue while changing the SAPSR3 schema password, other than default password "SAP".
For the issue i suggest you to follow SAP KBA 1576837 - ORA-01017: invalid username/password;
& notes 1534597 - Using such special characters as "@" in a password
(Assuming you may be using special characters while changing the password as desired,apart from the default one i.e SAP ).
Addition to it you could also refer note 1617976 - Case sensitive logon with Oracle 11g
Hope your issue will get resolved after following these.
Good luck !!