I am making an SDI application with split windows and different views for each side, like Windows Explorer. I am having troulbe derving the CTreeListView classes. I must reference the CList/TreeView derived class to set the runtime class in CreateView. I included the header files for those classes in the implementation file of CMainFrame. When I build it gives me the error: "CTree/ListView:base class undefined" in the header files of CTree/ListView.