[ns] a problem "_o38: wrong # args" when trying to let a node join the network:please help

[Nadine Chen]

Hi all,
I  tried to let a node join the network after a given time  by this command:
$ns_ at 10 [set node_(1) [$ns_ node] ] 
but  I have this error:
ns: _o38: wrong # args: should be {_o38 message ?args...?}
    while executing
"_o38"
Have you an idea about this error and how can I fix it?
is there any other command that let a node join the network after some time?
please help me.
thank you very much.