Switch to another modal dialog in MFC

I have a modal dialog. I open another modal dialog using DoModal, so that there are n开发者_运维百科ow two dialogs, one on top of another. When I then close the top dialog by clicking okay, I get an assertion error for line 896 of mfc90ud.dll. How can I fix this?

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Hi probably you did not set parent for your child dialog

CMyDialog dlg(this);