I recently purchased 2 Ultra 64GB micro SDXC cards (not a retailer/reseller) locally and in sealed packages, and find I’m having many issues with writing data to them. Both my Panasonic HD camcorder fails to recognise either card and so does my Canon DSLR. I thought this may have been because I was using an micro SD to SD adapter, this is not the case. I tried writing 18GB of data from my PC to either card and it fails. I’m currently testing card #1 with h2testw (Ver. 1.4) and it’s not looking good. Both cards seem to have serial numbers on them, but of cause I can not verify these numbers. Any suggestions please.
You can verify the authenticity of the cards by contacting SanDisk Tech Support and providing them with the serial numbers.
If they are indeed genuine but defective, they can also then arrange to have replacements sent to you.