SDHC UHS-I issue?

I have been using two Sandisk class 10 UHS-I cards in my 6D for about a year. The cards still work fine IN THE CAMERA. I tried them in my 60D and they work fine there, too. When I put them in my computer, I get all sorts of card errors: no card, no photos, format card?, and such.

I have a brand new laptop and the cards work fine in that, too. Reading, writing, formatting, whatever.

I reflashed the 6D firmware. Curiously enough, I could not use the Sandisk card. After I formatted the card in the computer, and put the firmware on the card, the camera threw a "bad" card error. I put the firmware on a different card and it updated fine.

I did some checking online and found out that some older readers struggle with UHS-I. Does this make any sense? The cards worked fine for almost a year, with over 5,000 shots on my 6D. Now they start acting up, ONLY IN THE COMPUTER. It is interesting that the computer can't read the cards EVEN IF I LEAVE THE CARD IN THE CAMERA AND USE A USB CABLE. Do I need new cards, or a new computer?

UHS-1 is the specification of the SD interface. Supposedly, all UHS-1 device (cards and readers) should be backward compatible. Meaning up on inserting the card into the reader or camera, they will negociate the proper interface protocol.

and yes, card reader manufactures usually do not follow spec as strictly as card manufactures or camera manufactures. So worth a try a new card reader

My computer won't read the UHS-1 cards even if I use a USB cable from the camera to the computer. The cards work fine in all my cameras, and in other devices. The computer reads 60D & 6D files off my non-UHS-1 cards just fine. This issues just popped up. I've been using these cards in my 60D & 6D for almost a year. Now the computer can't read them.

Older card readers might have some issues if they were not properly built to spec.