http://pastebin.com/V4mCETFj

Are you in lightweight mode? Because you should never edit stuff in lightweight mode.

I already solved this issue, it turns out that when you remove a mod that has an item in an item generator, the associated generator will crash. Would it be possible to add an option on all versions to automatically remove non-existent items from generators?

That's already in 1.10+ (iirc - if not I'll add it later). I won't do it for 1.7-, but you can fairly easily manually remove the item before saving.