Also EndGraphics is the opposite of Graphics NOT Graphics3d!
What sunteam is tring to tell you is - EndGraphics() should be called before you reinitialize another Graphics3d() command. Alt-tab works with windowing because the application window retains activeness even though its minimized or reduced ... this is not the case in full-screen mode as the window loses priority and being its' a Dx window it may/will cause things to act screwy... Not a way around this im afraid.. We actually need a disable alt-tab approach as discused in earlier topics.
Besides changing ScreenRes without restarting the app is not a good idea(with blitz anyways)..