[ns] first example problem

[Vaia Kaliva <kaliva@ics.forth.gr>]

Hello,
        I am trying to run the first example from the tutorial but I keep
getting a message like :

--- Classfier::no-slot{} default handler (tcl/lib/ns-lib.tcl) ---
        _o12: no target for slot -1
        _o12 type: Classifier/Hash/Dest
content dump:
classifier _o12
        0 offset
        0 shift
        2147483647 mask
        2 slots
                slot 0: _o37
                slot 1: _o19
        -1 default
---------- Finished standard no-slot{} default handler ----------

after the command  % $ns at 0.5 "$cbr0 start".
I use ns-allinone-2.1b7a, any ideas?

thanx in advance
Veta