i am getting "error when calling class $cls: $args" when i try to run my CRCN MRMAC.tcl file.please help me to resolve.

num_nodes is set 10

(_o3 cmd line 1)
invoked from within
"_o3 cmd add-channel 0 _o13"
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" $..."
(procedure "_o3" line 2)
(SplitObject unknown line 2)
invoked from within
"$ns_ add-channel $i $chan_($i)"
("for" body line 2)
invoked from within
"for {set i 0} {$i < [expr $val(ni)*$val(channum)] } {incr i} {
$ns_ add-channel $i $chan_($i)
}"
(file "MRMAC.tcl" line 50)