I tried this but I get the same error. What I did exactly is this:
Extracted ChocoEdit to a folder on my Desktop.
Copied Chocorpg from my /Documents folder and pasted it to the same folder on the Desktop with ChocoEdit.
Ran ChocoEdit and tried loading Chocorpg.
Since I wasn't sure if it's supposed to be editing Chocorpg or Chocorpg.ff8, I tried again with Chocorpg.ff8, but I got the same error.