[ns] NS multicast check question

[Darshant Bhagat <bhagatdb@cs.purdue.edu>]

hi NSUsers,
   I am trying to put a check in ns-node.tcl as follows : 

Node instproc entry {} {

        $self instvar ns_

        if ![info exist ns_] {
                set ns_ [Simulator instance]
        }
        if [$ns_ multicast?] {
                $self instvar switch_
                return $switch_
        }

        ....
}

it gives me a valid simulator instance..but 
then gives me an erros as follows : 

invalid command name "_o11 _o4"
    while executing
"$ns_ multicast?"
    (procedure "_o23" line 10)
    (Node entry line 10)
    invoked from within
"$self entry"
    (procedure "_o23" line 4)
..... 


can somebody please help me.

thanks in advance for all ur help,
Darshant