Which hack could be causing this problem? Yes, I know, I could take out the hacks and mods one by one, start the game, and check it out but what can I say.......
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Hopefully the link JennyJenny provided will solve your problem, but if it doesn't - and especially for future reference - I wanted to call your attention to the binary search. As you're new to the site (and mention having to sort through files singly) you may not be familiar with the concept. It's a simple procedure that sounds like it'll take for-freaking-ever, but it does not. It is a simple technique that generally only reqires a few restarts of your game.
First, remove your entire Downloads folder (and any other CC you might have stashed elsewhere) to your desktop. Restart and see if the problem persists. (You've already done this part, verifying that the problem/conflict lies with something in your downloads).
Once you've identified that the problem is download-related, put *half* of your downloads back in. Problem file not in this half? Switch halves. Problem file is? Moving on, then...
Take out half the remaining files. Problem file in which half? Switch or move on... Rinse and repeat as needed.
Yes, it looks like this will take forever, but it's a LOT faster than a move random by-file search. Say you have 1000 files in your downloads. Then you narrow it down to 500; then 250; then 125, 63, 32, 16, 8,4,2,1. Around 10 restarts to locate one file among a thousand? Very efficient. Like I said, I hope JennyJenny's link gives you the solution, but whether or not it does, this binary search is a dance we've all had to do one time or another. It is a useful procedure to keep in mind for future problems.