can't start rb module

[Oscar]

6> rb:start([{max, 20}]).
** exception exit: {noproc,{gen_server,call,
                                       [sasl_sup,

{start_child,{rb_server,{rb,start_link,[[{max,20}]]},

temporary,brutal_kill,worker,
                                                                [rb]}},
                                        infinity]}}
     in function  gen_server:call/3



what does the above exception mean?