error in nam

[humairaafzal73]

hi,
whenever i run nam in ns2, following error appears.
nam:
[code omitted because of length]
: no event type or button # or keysym
while executing
"bind Listbox <MouseWheel> {
%W yview scroll [expr {- (%D / 120) * 4}] units
}"
invoked from within
"if {[tk windowingsystem] eq "classic" || [tk windowingsystem] eq "aqua"} {
bind Listbox <MouseWheel> {
%W yview scroll [expr {- (%D)}] units
}
bind Li..."

----help me in this regard
---Humaira