Class A

Firstly, the class A issues, which crash at the start of the game, stoping you even possibly getting into the editor.
(Read; we're so screwed!)

Darwinia Crashes when... I start it, or when I make a new profile

9 times out of 10, these will be spelling related.

Start it: One of the following error messages usually pop up;

Invalid shape file specified - spelling mistake in shape name, haven't put .shp on the end
Invalid map file specified - spelling mistake in either map file or reference to it in game.txt, OR, you're having some sort of profile collision.
Building ID not unique - Ususally a result of editing a level with dynamic buildings with a game.txt that has that level's mission set to null (eg when you've gone back and changed a finished mod); go to the end of the map file in question and ajust the building ID (eg by adding 100 to it)

Remember - some file systems are case sensitive - make sure the cases of your map names all tie up if people are reporting issues like this!

Creating a new profile:
Game.txt typo, probably a more major, structural one, than an actual script command typo.

And actually, that's it for Class A issues.