I don't know about a "light" six switcher. I personally own the heavy version. If your six switcher is the same as mine, you will note that the cart fits in a lot deeper. Mine fits fine although it seems as though not as much of the circuit board is fitting into the slot. (Does that make sense?) Is it possible that during moving of, maybe even during the manufacturing of the unit, that the hardware inside is off kilter? this could possibly create reduced area for the cart to slide in. Activision and Imagic carts on each side seem to "bow out" to an edge. (Hmmmm....Does that make sense? I know what I mean but does anybody else?) Good Luck!
RE: 6 switcher doesn't like Activision carts