Make sure your antivirus does not flag "Assembly-CSharp.dll" only thing that makes sense.
(this might mean to set up a exception for it in case it does flag it)
A lot of AV will flag a good portion of these games as false positives. I have yet to come across a link on this site that is an actual virus. So you need to make sure that your AV makes an exception because they will fuck up these games. So just make the exception and redownload the game. If that doesn't work it might be a problem with windows (assuming you have that as an OS) or your computer.
Yeah, see, it let's me do ALL the installing, but at the very end, it tells me the file doesn't exist. I've literally opened the file to location and watched the file just disappear as it gets to this part. No flags from AV or anything, just poof, gone. I had been using the old "Assembly-CSharp.dll" from the previous versions to bypass this issue, dropping it in the install location, but now it just gives me the bugged game. And yeah, I'm running Windows 7.
And again, thanks for the help so far and continued.
(nvm, I got it figured out. My AV wasn't alerting me to the catches for some reason... last update kicked in "Don't show alerts" in options.)