See final turn of game 121987560
I played a spell scroll, but it had 0 cost so there were no cards that I could gain, since nothing costs less than 0. I couldn't proceed with my turn or take any further actions. Luckily my opponent granted an undo to let me get out of this situation, but this could catch someone.
(I guess I could have specified: in this game I lowered the cost of spell scroll to 0 with inventors. Presumably this could happen with bridges, bridge trolls, highways, quarries, or anything else that lowers cost of cards as well)
Thanks for reporting!
That is a bug that has been reported once before, but it hasn't been fixed unfortunately.