Oh my god.
So I have a finished novel for which I am sending out queries to agents.
Most agents only want to see the first five or ten pages, but I came across one that wanted the first 25 pages, and one that wanted the first three chapters.
Well, I have two laptops right now since one of them is still technically useable, but on its very last legs and in imminent danger of dying forever. Due to a big complex thing about NaNoWriMo and Scrivener and Microsoft word, I had the full, final edited version of the story on Scrivener on Laptop 1, but had to put it into manuscript format on Laptop 2 in Word.
So I compiled the Scrivener files and sent them to myself, and began working on it.
Only to discover, to my horror, AFTER I sent the first 25-30 pages to two different agents, that I was using the wrong version version of my novel, and had completely skipped chapter 2. It just jumped straight from chapter 1 to chapter 3, only I also mistitled them, so it wasn't even like the agent could have noticed what happened, since chapter 3 was now titled chapter 2, but a huge chunk of the story was just missing.
I'm seriously kicking myself right now. I'm just lucky I caught it when I did, and I only messed up my chances with two agents, rather than the next dozen.