This file has currently been set to hidden by the author of the file. You cannot look at this file page or download any files relating to this file until the author makes the file visible to the public again.
The reason given by the author is: Valve has switched security certificate provider from Verisign to DigiCert.
As a result it is no longer possible to downgrade XComGame.exe to any previous version.
TLDR: Game over, move on.