Not sure how it happened, but early game I got two stacks of Iron Ingots going. One of a single ingot, and the rest were in the other stack. The game wouldn't understand that there were two stacks and thus wouldn't let me build the Forge. I tried tossing one from the single ingot stack, and it tossed from the larger stack. Ended up having to toss them all and recollect them to get them all in one stack and then continue on with progression.

Just some info in case there's a bug involved. I honestly couldn't tell you how it happened.

EDIT: It seems like there is a huge issue with inventory. Things keep double-stacking, disappearing, and reappearing. Makes the game almost unplayable. Inventory gets filled up pretty quick, maybe implement a banking or chest system? (maybe one's already put in, wasn't able to get far enough to find out)