Card keeps preparing?

I have a Ultra 64 GB microSDX card that i bought in may off amazon. Yesterday it started poping up on my phone that it was preparing the card, as if i had just put it in the phone. Since all of my music and things are on the card it would stop playing, which is really annoying since it keeps doing this every few minuets. I though it was just my phone, but i put the card in another one and it does the same thing. How do i fix this?