Hi Myrddrael,
Yes it most likely one of your new unts is causing the CTD. As MonkWarrior says there's only one way to edit, (once you've found errors) and thats go back to the begining and do it step by step. If the games loading, your unit_prod file is probably OK.
Scripting errors within the unit prod, normally prevent the game from working at all. The error is more likely to be with names, descriptions or the unit bifs in Infopics or Review panel. A good way to isolate the unit that has the problem is to open your new units in Custom battle. If/When a CTD occurs "Eureka" you've found the critter.
Happy hunting