You can test the card's read and write speed on the computer. If it's not as advertised, send it back and get a different one, but that doesn't save your master, unfortunately. Check all cables and connections, especially if you can't find fault with the card under testing.
Even a class 2 should be fine for anything the M10 can muster. I use a 16GB Sandisk M2 card, and it's slower than heck on transfers but works fine in the machine.
(wow, I think I paid $16 for my M2 card, and they're 50 bucks on amazon now!? Stick with the MicroSD cards at that price!?)