Inheritance Problem in BPL, help!!!

Hi,

My apology for re-posting but i'm still having problem on this :-(

Host App
========
units
  MainForm  {MDI Form}
  MainChild {MDI Child}

BPL
========
requires
  VCL50
contains
  MainChild
  ActiveChild //inherited from MainChild

in Host App codes:

var
  AForm: MainChild;
  ...
  Handle := LoadPackage('BPL')
  ...
  @MakeMDIChild := GetProcAddress(Handle,'CreateChild');
  AForm := MakeMDIChild;  //create a form of type ActiveChild    
  AForm.Filter;   //implemented virtual/abstract method declared in MainChild

On call to Filter function, an abstract error is raised, though
it is already implemented in ActiveChild class. Why? appreciate
very much if there is another way making sure that inheritance
is not lost using EXE and BPL.

mthanks.
Jimar