Help! - SD Card shows 2.35 GB used but photo shoot can't be found

That explains your difficulties. The UHS-1 cards use the very latest high-speed semiconductor technology, and must be used in adapters and USB interfaces which are capable of driving their high-speed signals. They are prone to fail whenever you get them near a computer. I use SDXC-certified USB dongles from KomputerBay (on Amazon) which seem to have a low failure rate.In my laptop I use a Transcend Expresscard reader, which also has the advantage of reading their data at about 40MB/s, twice the rate of a USB dongle. And when you are copying 32GB of video, that speedup can save you hours...