Since you've installed GOTDs in the past, I won't bother you with any of the basics. It **sounds** like security software interfering -- if that's the case, it normally works to boot into Safe Mode with networking.
Why that works is that in Safe Mode the services that run with most security software aren't running. Usually you can't turn those services off while Windows is running normally as a security precaution -- if you could turn those services off, so could mal-ware.
Why today & not in the past? Security software is constantly updating, so it could be something they added or possibly a bug in the latest update.
Why the message about files being corrupt? The way a GOTD works is that once the date's verified, the actual installation program is unpacked into memory. If security software interferes with that installation file or files, they no longer match what setup is looking for, & when it can't find what it's programmed to find, it tells you the files don't match by saying they're corrupt.