Can anyone help me to fix this problem

I can using rman target=/ command without any problem

but when I'm using rman target sys/change_on_install@student

I'm getting this error


RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-00554: initialization of internal recovery manager package failed
RMAN-04005: error from target database:
ORA-01017: invalid username/password; logon denied


Thanks in advance