There is no sales price within filter filter sales code ",item no xxx error proplem

Hi guys i have problem when i make return order to sales order then make function - copy document select posted invoice

and select invoiced sales order document then OK

message error show to me :

http://www.mediafire.com/download/3kcfy5nc5ckyz3a/sales_return_proplem.bmp

and this is code in debugger

http://www.mediafire.com/download/izcv5c4b7icfctt/sales_return_order_code.bmp

My message error is :There is no sales price within filter

filter sales code ",item no xxx

How i solve this problem

thanks