报错：cannot create forms. No MDI forms are currently active(100分)

一个MDI应用程序，在不选择“Build with runtime packages”时编译程序，在打开MDI窗口时会报错：cannot create forms. No MDI forms are currently active，但在选择“Build with runtime packages”时编译程序时，却能正常打开MDI窗口，请问高手这是什么造成的？

var
pp: PLongInt;
/////
pp := @(Application.MainForm);
pp^ := LongInt({你要的owner窗口});
试试