sha_mac erlang call

gistfile1.txt

1> crypto:sha_mac("my_key","GET\n\n\nThu, 02 Dec 2010 10:05:01 GMT\n/").                                  
** exception error: bad argument
     in function  port_control/3
        called as port_control(crypto_drv02,11,
                               [<<0,0,0,6>>,
                                "my_key","GET\n\n\nThu, 02 Dec 2010 10:05:01 GMT\n/"])
     in call from crypto:control/2