Same exact problem here with my 16gb MicroSD HC card. Called : 866-726-3475 and 45 minutes later they are replacing my card. There is a lifetime warranty on the card. The call center is in India so be prepared to be very frustrated and repeat yourself numours times! The technician I spoke to treated me like I was quite computer illiterate. I had to use the phonetic alphabet (alpha, bravo, charlie…) so he could understand me… Overall this will be my last Sandisk purchase for lack of customer service!
edit : looks like I am going to have to call them back as the guy setting up my RMA hung up on me. JOY…JOy…joy!