My treasury when it started to drop was in the mid-hundreds (I try to adjust spending up regularly to avoid letting the treasury get too big). I did have an event that dropped me into negative territory but I had come back out of that.
I did exit the program at one point and later started from the saved game and noticed that my treasury was losing money instead of gaining. After it fell into negative, it went back and forth as I adjusted spending down, taxes up, but it finally fell to the around -500 mark, where it's been hovering around -500, sometimes as low as -900, sometimes as high as -300. Constructors on their way to the second and third morale resources (after the initial constructors secured them) may not have arrived until after I noticed morale dropping, but the added mining seemed to have little or no positive effect.
I may have certainly made some other fatal mistake (I had a *lot* of planets--my first gigantic galaxy and planets everywhere, all average aliens, two evil, two good, one neutral) and everybody who hadn't built a couple of defenders and something heavier was busy building constructors, but most planets were in the 90s and 100s (still building defenders) before I found the first morale resource and it stayed that way for a while. I also always stop military construction when planets drop below 70 after completing a ship, but that didn't seem to stem the tide.
Restoring from saved games have often seemed to precede big changes, but that could be as much imagined as real.
Still to this point my economy in the annual reports is 78, I have the biggest military, the most influence (and no influence resources until the last year or so) and until the real bottom fell out of the economy, I had the best economy, the best production and was further ahead technologically. I waited longer than usual to get to the first habitat improvement, but there were always morale builders in between the productivity builders in the social queue.
By the way, in my previous game, there were never any elections no matter what kind of government I had. Unfortunately, there have been elections in this game...
-Robert