In our application, we have property page created in the main. When the use click the tab of the page, its handle is passed to DLL and a window is created for the page in DLL and the handle passed to DLL become its parent. When the App exit, the window gets destroyed and crash occurs because the window handle map is NULL. In this sceanario, i like to know what is the root cause of the crash? (if i stated the problem clearly). I would greatly apprecite if any expert explains the cause of problem. And how to go about getting infomation in resolving the problem.