I was playing as the Kingdom of Brittany. I had managed to expand into Wales, SW Ireland, Normandy and Anjou. I had a queen who reigned for a long time who created a university and oversaw much of said expansion. When she died my treasury was flush and I had no sizable expenses. The inheriting son had spent considerable time in Bulgaria and had converted to Orthodox Christianity and was quite insane. This in of itself was no difficulty except suddenly there was a mystery expense on the treasury of 16 per month that I could not explain or dispense with. I had no troops raised and without an effective ledger in this game, no way to determine what was causing this drain on my treasury.
Said son died shortly thereafter and his Roman Catholic heir took over, but the expense remained, meaning neither his father's religion nor insanity was the source of the mystery fee. The new king was no financial wizard so this expense was crippling. Lacking any way to deal with it, I called it quits.
Is there any way to determine what is incurring expenses in this game? There is something called a 'ledger' but little of it deals with money.