I have no idea about the tax glitch, but from what you say it appears that you were only about 100 bc/month in the black after ten years of game time. If that's true, then you have not built a proper economy: you should be making tens of thousands bc profit per week after just a few years, not 100 bc/month. After ten years, your economy should be so strong you wouldn't even notice a 1600 bc tax.