Debug Assertion failure

Hi,

This might be a stupid one but i am new so please bear..

I am trying to create a simple program using MFC which has a Parent Main Window and a Child Window, which apeares when user clicks on one of the menu items.

When i kept that chaild window as a simple child window which can move in the parents client area only.This works fine.

However when i convert the same child window to a "popup window" (using WS_POPUP flag ) the programes gives me an "Assertion Error" while i try to execute the program. (The program build fine).

The same thing happens when i try to create a fixed child window (which covers the entire Paretn client area).

I am using Visual Studio .Net to write these programs.

So i am not sure what am i doing wrong ? any help will be highly appreciated.

Thanks.