Everytime after a city have built too much rum distilleries, this happens.
Water (and food) is "profitable" business. (smirking)
Side note, this is the case that when city has totally ran out of water, and has 18 rum distilleries.
BTW also a reporting a problem, not sure is that the city out of funds or a bug.
When the sum of profit in a single trade is too large the transaction will not occur even if you click sell.