I have had the same problem with this Quest and another one too.
After MANY and MANY tries i was able to go on with the mission and i tell you how...
When you go to Yonda, before talking to her, open the "give" menu and put the molten irons in it, without conferming the trade yet.
Then talk to Yonda... BEFORE she tells that she needs 2 molten irons and 100 trias, click to confirm the trade of the 2 molten irons, and that's it! She accept them!

At least it worked for me that way...

This way i could move on in another stuck quest:
Chrosor Soran has difficulties training.
When you talk to Brado about weakness he says many things and then he asks if you want to help him and you have to answer Yes, but when you say Yes he doesn't understand. But if you say: about weakness and immediately after you say Yes, without waiting for Brado's dialogue to appear, he will accept your cofirmation and the quest will move on.
But now i'm facing a similar problem with another quests, and this time my "method" doesn't work

In the quest:
Lorytia Starhammer and the Clan reunion, when you return to Trasok with the letter of apology, he needs iron ingot and gold ingot, but he doesn't accept them... The problem this time consists that there isn't a dialogue that triggers Trasok's request for ingots, but he requests them when you give him the letter... so i'll need another letter of apology to trigger his request again and quickly give him ingots. But how to obtain a new letter??? I tried to talk to Lorytia again but she doesn't give me another one, so this time i think i'm really stuck... If anyone could help that would be greatly appreciated!
Ty and sorry for the length...