Hmm.. Still getting the same error.
I went and tried another method using the same flash drive (link in 1st post in this thread), which I think is the same thing it's just a script and it seems to work fine now. No idea what the problem was.
Let me do some digging.
UPDATE TO ALL GUIDE USERS: IF YOU ENCOUNTER THE SAME ISSUE AS ABOVE, PLEASE USE THIS ALTERNATE METHOD:
[URL="https://forums.macrumors.com/threads/1409416/"]OS X Mountain Lion - Alternate Flashing Method[/URL]