Help with Downloading OST

I'm currently downloading the Ocarina of Time full OST from the Music part of the site. I'm doing this each song individually for my computer, as I can't download them all for phone.
I'm alright with this, except the fact I'm getting a message come up~
When I downloaded the first song, it downloaded perfectly, no problems.
The second, third, etc, songs that came up; a message comes up when I attempot to download saying (exactly):
"Your Download Key has expired. If you wish to download this file again, you must renew your Download Key. Press OK to renew your Key."
I then click the little "OK" button underneath, press "Download to computer|" again, and everything is fine until i try downloading another song, on which this happens again.
Any ideas why this is?