I have an MFC SDI application in VC++6. Data is read from disk in the Doc, converted, and displayed in the View. I have implemented a CDialog, launched from an entry on the main menu, in order to permit the setting of data display options. By including the CDialog's header in the Doc, I can successfully access the member variables of the dialog in a Doc function which instantiates the dialog. Code compiles ok, dialog can be started, but when any writes to a dialog member occurs (Editbox, Listbox), I get an Assertion failure. In release mode, nothing happens. Two days of searching have not helped find what must be some simple structural error.