DirectX + MFC problem

I created a basic DirectX class that sets up a Directx object and creates a primary and secondary buffer and then used it in a basic MFC app. When I tried to lock the primary surface on the OnPaint event of the main window I get an Access Violation error (C000005). I''m sure there is a strong possiblity that I am doing something wrong but i''m just not sure what. The class works fine when I use it in a plain WIN32 app. Oh, and I forgot to mention that it''s full screen exclusive, but since MFC won''t let me use a popup window style, it shows the window. Anyone know what could be causing this Access violation error? Thanks, Phillip