I inserted the microSD card into my Mac and it showed up with 4 partitions. I tried reformatting myself (BTW I work with media drives as part of my job, so this should have been easy for me) but it didn't work. So I called Sandisk customer support. I told them my problem and my computer's specks, so they knew I had a mac. They sent me third party software for a PC. I called back and they told me to go to a public library to reformat it on one of their PCs. I also bought the 400gb card and have had no issues with it, so take that for what it's worth.