I keep getting "ERROR Cannot Connect to iTunes Store" when attempting an in-app purchase.

I've been trying to complete an in-app purchase within the game "Nemo's Reef" for over a week and repeatedly get the same "ERROR Cannot Connect to iTunes Store"

I've tried a real close for the app, restarting my device (iPhone 5), enabling and disabling restrictions - I DO NOT have in-app purchases restricted under settings-general - restrictions - in app purchases.

I purchased a book in iBooks this morning - my card was charged and the item downloaded perfectly. I have tried the purchase on WiFi as well as Cellular but neither work. I've also tried turning off my WiFi completely, still doesn't work.