[ns] problem about wireless2.tcl in the tutorial

["ncs" <ncs@hbhs.buaa.edu.cn>]

hi all,
I want to do some change in wireless2.tcl in the tutorial.
but there is a strange problem in the script.
At first it works correctly.
when i change it (just change the comment),it can't work.
the error is following:

num_nodes is set 3
warning: Please use -channel as shown in tcl/ex/wireless-mitf.tcl
__FAILED_SHADOW_OBJECT_
    while executing
"error "__FAILED_SHADOW_OBJECT_" """
    (procedure "set-hieraddr" line 4)
    (SplitObject init line 4)
    invoked from within
"set-hieraddr init 1.0.0"
    (Class create line 1)
    invoked from within
"AddrParams create set-hieraddr 1.0.0"
    ("eval" body line 1)
    invoked from within
"eval [list $self] create [list $m] $args         "
    (procedure "AddrParams" line 5)
    (Class unknown line 5)
    invoked from within
"AddrParams set-hieraddr  [$BS(0) node-addr"
    ("for" body line 3)
    invoked from within
"for {set j 0} {$j < $opt(nn)} {incr j} {
    set node_($j) [ $ns_ node [lindex $temp \
    [expr $j+1]] ]
    $node_($j) base-station [AddrParams set..."
    (file "wireless2.tcl" line 138)

who can tell me what i can do with it?
thanks in advance.