Lexar 64GB or 32GB

[5Dme]

Hi everyone, I'm new here so I hope to learn a little and maybe give something back!

I have ML on my 5D Mark II(came already installed on the camera when I bought it secondhand) I decided that I needed to put it on my new 5D Mark III so I down graded my Mark III firmware from 1.2.3 to 1.1.3 before installing ML, the problem is that I tried installing it using a Lexar 64GB 400x speed SD card and no matter what I tried it wouldn't install for me. I then ran some tests on the card to see if there was a problem with the card and it seems to be fine!

I then tried installing ML with a Lexar 32GB 400x speed SD card which worked a treat! So my question is, is there a known problem with installing ML using a Lexar 64GB 400x speed SD card?

Just on a different note, I don't know how I managed before ML...