I have had this problem a few times, and have investigated it a little.
Long description now, short solution at the end.
Disclaimer, this description includes my assumptions, based on observations. Verifying with sources is too difficult.
Things I tried when this first happen:
1. Delete the file
2. Use verify files
3. Uninstall and reinstall
4. Install on another PC
Nothing worked.
The way I assume the update system works is this: You download a manifest of files, each including some kind of hash for each file. The updater compares the hash in the manifest to the one calculated from the local file. If there's a difference, the file is downloaded. Another assumption is that the download is done via HTTP (regular web protocol).
Now to the kicker, the only explanation I could figure out that could cause this is if the local ISP was caching the previous version's file, since the server didn't specify a "do not cache" on its files. This means that the updater was downloading the old version of the file from the ISP instead of from Frontier. After the download, the hash value was compared, and it failed causing the error we saw.
The solution, which gave me some corroboration to the hypothesis, was using a VPN to relocate my connection, after which the update went fine.
(I opened a ticket and described this to the devs, but I guess they have priorities)