Yamaha PSR-S900 unable to see midi files on usb stick

Hi,

I have just purchased a psr-s900 and was hoping to upload some midi files I have downloaded from the yamaha website. I have loaded these onto a usb stick and tried to upload to the keyboard, however the keyboard doesn't detect any files on the memory stick. I am able to write to the memory stick however and these files (midi) can be seen on the computer.

Please help! Thanks,

Angela