[ns] What's wrong with my scheduling algorith?

["gbsource" <gbsource@uestc.edu.cn>]

Hi
I am a ns-2 user and I am interested in traffic scheduling. I found
Markus A. Wischy 's page on virtual clock in ns-2.
I have downloaded source code in my ns-allinone-2.1b5 , and doing the
follows in ordor to add virtualclock into my ns:

1.Add to the Makefile in the ns2 directory in section OBJ_CC following line:
virtualclock.o VC_Queue.o \
2.Make ns.
3.Add the following line to the file ns-default.tcl in the tcl/lib directory
of the ns package.
Queue/VirtualClock set print_info_ false

But when I tried to run his test.tcl, it doesn't work. The beginning of the
tcl script is shown below :

# A test for the Virtual Clock scheduler

# create new Simulator
set ns [new Simulator]

# create network nodes
set node1 [$ns node]
set node2 [$ns node]

# create link between the nodes
set link1 [$ns duplex-link $node1 $node2 100kb 10ms VirtualClock]
# set the queue limit
$ns queue-limit $node1 $node2 10

# get queue from link,
set vc_queue [    $link1 queue]
~~~~~~~~~~~~~~~~~~~~~~~~~~
There is an error when execute here, it says,
invalid command name  ""
while executing
"$link1 queue"

Does anyone know what's wrong with me? Is there anything missed
when I tried to add virtualclock algorithm? Or is there anything wrong
when I get queue from link? Please Help me!
Thanks in advance.
Xiang Yu