Tk::Error: Can't call method "curselection" on an undefined value at C:\Users\Ettore Vecchione\Desktop\ORG CHART APP\chart.pl line 135.
 Tk callback for .frame.button1
 Tk::__ANON__ at C:/Perl64/site/lib/Tk.pm line 251
 Tk::Button::butUp at C:/Perl64/site/lib/Tk/Button.pm line 175
 <ButtonRelease-1>
 (command bound to event)