Purchased music can only be downloaded once.
You can access ProStudioMasters from multiple computers, but once a track has been downloaded to one computer it will no longer be available for downloading to another. You can transfer downloaded music to other devices for playback, but remember, this must be for your own personal use only.
On a related note, we strongly recommend making a backup of music you've downloaded. This will help protect you in the unlikely event of a hard drive failure on your local machine, or from accidental deletion by you or others with whom you share your computer.
In rare cases we may be able to re-enable downloads for previously purchased music. If you can make a plausible case, open a support request (ask a private question) and we'll try to help you if we can.