There was a similar discussion on the following thread:
Adamantine Forge Cannot be used twiceI realized there were two mithril veins and I had missed one. I cannot interact with the crucible and the mold-thing is stuck. I think this is not a bug so much as it is a flag. Let me elaborate. It locks the forge when there is no more mithril in your inventory. if you have two, use one, you can use it again on the second, but if you only had one to start with, the game doesn't recognize that you could go get the other and come back.
My question for you is, the very first time you used the Adamantine forge, did you have both pieces of Mythril ore in your inventory? I've beaten Grym on 5 separate playthroughs now on Balanced, Tactician and Honour modes. The only time I was locked out, was when I only had one piece of mythril in my inventory the first time, and had to go back for the second piece.
