When I select the GPS function of the my iFly 520, a pop-up message says I need to insert a valid memory card. I have been using, and updating, the same SD memory card for over a year with no problems. In fact, I had just returned from a successful flight using the unit only an hour before when it first occured. I tried ejecting and inputting the card several times to no avail. When I went to see if my MAC could read the card - it did not appear in Finder like before. Since my computer did not recognize the card, I summized it had to be a memory card problem so I called the company and had them send me another 8GB SD Card with updates (at a charge to me)... when I inserted the new card the unit did not recognize the card...nor did my MAC. The sad thing is the unit and card worked wonderfully during my last flight and nothing was done to either after turning the unit off. Has this happened to anyone else???