Just had the same issue.
All fixed now : )
I am assuming that we have had the same problem.. Accidently deledting music from iCloud?
Go to 'iTunes Store',' Account',
Under 'iTunes in the Cloud' (section) there should be something about hidden songs or purchases.
Go in there and select the purchases to 'un hide'.
Then go to 'iTunes Store',' Purchases'- They should be available for download : )