I recently acquired an enchanted book (Flame I). Since I heard that you can enchant a sword twice or more times with enchanting books, I tried to enchant it using an anvil with my diamond sword (already enchanted with Sharpness something, I think). When I put the two items in the slots, all that happened was that a big red cross appeared in the output area. So, my conclusion on this problem is that I don't have the required level for enchanting it. Please help me figure this out. Thank you.