Note: Underneath the cartridge tray is a black trapezoid-shaped tab/lip (see marker). When properly assembled this tab/lip goes below the motherboard and shielding as seen here.

During reassembly, make sure you orient this tab underneath the motherboard in addition to orienting the tray on top. Failure to do so will bow the cartridge tray and place stress on the component, causing the cartridge spring mechanism to bind.