rman initialization with insufficient privilege

I tried to connect rman to target database and run the configuration. However, I am getting the following error:

Recovery Manager: Release 11.2.0.3.0 - Production on Thu Jul 26 21:26:32 2012

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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-01031: insufficient privileges

I am using sys user. How can sys not having privilege?

Is there anything wrong with my command?

rman target sys/password@vision nocatalog