Lost production

[Eto]

Greetings, folks. New to the game, looking for an answer to a question I have.

Sorry if this has been asked....but...from time to time it tells me construction cannot continue on x project. Production is converted to gold, etc. I know this happens when someone finishes a wonder before I do, but often this isn't the case. What are other reasons are there to cause this?

Thanks!

 

[KGrevstad]

It also happens when you lose a critical resource for a unit, like iron for swordsmen, or oil or aliminum for modern armour and such.

--Kristine

EDIT: Although I don't recall if you get a refund on your build investment in those cases like you do with Wonders.