Im am using Garmin Express on by MacBook Air to download a purchased marine chart update. On my first try it downloaded for about an hour and then just quit and said that the SD card was locked. I have now tried with three different miniSD cards but I get the same error before it even starts. Also the miniSD card does not even have a lock switch on it and two of the card were brand new out of the box and got the same error. Suggestions?