Is it possible the SD cards that are failing aren't properly formatted? From what I've read it is best to use a special format program rather than the one built into Windows. See
http://www.online-tech-tips.com/free...tting-sd-card/ for more info on why this is so and to get the special formatter program.
Another possibility is that there are lots of fake SD cards floating around, especially on eBay, even for brand-name cards such as Sandisk. See
http://www.youtube.com/watch?v=JcTYRblCfPg for a video about the fake cards or
http://fightflashfraud.wordpress.com...-32gb-sd-card/ for more discussion.