Bad rom after making changes with FF3usME 6.7

So my rom becomes "bad" after I make so many changes to it through FF3usME. The game runs fine until the game triggers the first battle in Narshe, then ZSNES crashes. Is there anything in usME that I shouldn't be changing that would cause this? Is it because I'm expanding the rom to 32Mb after I already make changes? (in other words, should I expand a clean rom FIRST before making any changes *at all* in order to prevent this?)

It's kind of hard to narrow down the problem if it's an individual change, because I've made quite a few changes throughout the rom. Any knowledge that anyone may have is much appreciated!

(and for the record, yes, the original rom is 100% clean)