[ns] Getting Error for simple Ping

[babak]

Hi all:
I make a new protocol. It is the same that ping protocol but with other 
name. I make the necessary changes in ns2 that  Marc Greis' tutorial said. 
But when I run the ping.tcl changing ping agent for my own agent, I obtain 
the follow error:

ns: _o59 send:
    (_o59 cmd line 1)
    invoked from within
"_o59 cmd send"
    invoked from within
"catch "$self cmd $args" ret"
    invoked from within
"if [catch "$self cmd $args" ret] {
set cls [$self info class]
global errorInfo
set savedInfo $errorInfo
error "error when calling class $cls: $args" $..."
    (procedure "_o59" line 2)
    (SplitObject unknown line 2)
    invoked from within
"_o59 send"

Thanks
Babak