I have a VX2 system and recently purchased a previously loved NT C MAP card M#US906LX3. I inserted the card with the unit powered off, then powered up the unit. The unit gives it's normal "beep" upon power-up and the screen color changes shades slightly but then does nothing else. If I remove the card the unit powers up as usual. If I insert the card with the unit powered up already the unit is completely unresponsive upon the press of any buttons. I am not very familiar with this unit as I just purchased the boat and any previous plotters I have had utilized pre-loaded charts. Am I doing something wrong?