"GameSpy Crash Fix"
As of December 6th 2012, GameSpy Arcade has shut down for the foreseeable future. S.T.A.L.K.E.R. - Shadow of Chernobyl however was never originally designed to be resilient against such events. As a result, the primary means of getting the game to start had been to disable all internet connections and re-enabling them once the game had started up.
A user by the name 'Davi' both informed me of the issue and provided a fix. It was as simple as copying over Clear Sky's newer, more resilient xrGameSpy.dll over and replacing Shadow of Chernobyl's.
A download link has been provided below to the fixed DLL file.