SD card read problems?

I have an 8 gig Lexor class 10 SD in my camera and yesterday when I cam to transfere some photos from it to Finder they didn't transfer. I was trying to drag/drop them as I normally do. Then when I tried to open a couple of the photos directly from the card it came up with the massage "The application can't be found" This is in our mid 2009 MacBook Pro 13 running Mavericks.

It shows the card in Devices and all of the files and folders. When it first happened I tried it in our iMac and there was no problems either with transfering photos, or opening them from the card. I then cleaned the card contacts with a pencil rubber (an eraser I think you call it over the pond?) and tried it again. It worked OK and I thought I'd cracked the problem, dirty contacts? Today it has happened again and this time the rubber doesn't cure it. I have tried it again in the iMac and it operates OK, transfere and opening from the card.

Some other cards work fine and some not, so now I am confused as I have not had any problems before and as far as I know nothing has been changed?

Yesterday it was a case of now it works and now it doesn't..

Any ideas please folks?

How old is the SD card? And is it a regular SD, mini or micro SD? How many times do you put and pull it out of the camera? More than the contacts, the SD flash has a finite life. The Class 10 from a reputable brand should last for quite a while..

I have no ral idea just how long I have had it, but it has been out and in the camera numerous times. I have always thought of Lexor as a good brand.

It's a standard SD, not mini or micro and I use 8 gig because when I bought it I could have had either 2 8s or one 16 gig and I sought the safety of two cards. Plus, the 8 holds more photos than I need so it suffices well. I always carry the second 8 gig and a spare camera battery.

What stumps me is that it is perfectly OK on our iMac? And to stump me further, we have just got back from our Thesday afternoon walk with our village walking group. A really nice 8 km walk on which I took 78 photos. I thought what the **** and put the card in the MacBook and it has worked perfectly. Transfered all the photos, opened then on the card and done everything it should have done!

My poor little brain cell hurts now!