Have the same problem but with my Mac Book Pro and Windows Laptop.
I actually have a Samsung Ultrabook with a MicroSD-Slot, where i used the San Disk Mobile Ultra 64 GB micro SDXC as second drive (SSD only 64 GB). As i had to send my Samsung Laptop for a service, i borrowed a Mac Book Pro from school, which has a SD slot. I used the SD adapter to try if it worked there and until yesterday it had been working great. Today neither the MBP nor my girlfriends Windows Laptop with SD Slot are recognizing the content.
Mac Book Pro says that the Medium couldn’t be read. The Apple SDXC Reader Media recognizes only a 32.1MB card. Only Option: Formatting.
Windows Laptop says the card couldn’t be read and only option is to format it.
As the card has very new stuff on it, i would prefer not to format it
Any suggests? Why are so many people having these days the same problems with this card?