have a doubt in binding listbox items in (WPF) using vb.net

PFA

Hi

   I have a doubt in WPF page.

  Actually in a pop up window page (WPF) ,im generating numbers in listbox ,
After generating in listbox,im closing tat window page (WPF),and loading those
generated numbers in Main Page (WPF) listbox.

but not able to do tat ,it shows error like in POP up window page(WPF)

regards

Naveen....