"Complete Album" Problem - "Purchase of this Item is not currently Available. This item is being modified. Please try again later."

I am trying to complete an album of which I bought 3 singles and every time I hit "Complete Album" for $4.83, it says "Purchase of this Item is not currently Available. This item is being modified. Please try again later." Ive tried multiple times over the past week and get the same error every time. Can anyone help? Thx