If with "take everything off and redoing all FSDT scenery from scratch" you mean you uninstalled/reinstalled everything, there's wasn't obviously any need to do that.
A crash which result in an error that doesn't even give you the ability to restart Couatl (usually it does, after showing the error), is usually fixed by exiting the sim, wait a bit to be sure it has closed correctly, and restart it.
In the worse case, you might have to restart Windows, but that's very rare.
