Had a similar use a while ago and this is the fix that Apple sent me -
Go to User(your home folder)/Music >Select/highlight your "Music" folder. You will need to go to external drive where your files are located
Then press Command-I ("Get Info" from the File menu), click on the padlock icon in the lower right of the new window >Enter your user password.
Click on your username just above the now-open padlock >Select "Read & Write" if it's on "Read Only," "Write Only," or "No Access."
Now having your user account with "Read & Write" privileges (it may have been this way already; still do this next step), click on the gear on the bottom-center of that window.
Click on "Apply to all enclosed items." When the pop-up says "Are you sure?" (or the equivalent), say "yes." This will grant access privileges to your user account for all the music files inside your music folder--all your iTunes stuff included).
Once the above instruction is performed, kindly try download the song via iTunes in the cloud and this below article will guide you on re-downloadng the track for free of cost: