Hi all,
I've been having this problem for the longest time. I used to play Xcom which I bought on Steam, and when it's available on GOG, I redownloaded and reinstalled using the GOG installer. Everything went well and smooth.
But when I start up the program, it immediately crashes after the introduction. Sometimes I could maybe luck-in and get to the main menu, but that's about it.

Through trial and error, I found that when I turned off my WIFI, then the game works perfectly. No issues in loading the game, and no issues in even running all my saved games that I had when I played on Steam or on GOG.

Anyone has any idea what led to this, or if there is patch for this??

Did you completely uninstall the Steam version before installing the Gog version —— including cleaning the Registry?
If your WiFi is part of the problem there is some trigger in the game where it is trying to reach a server. This would be standard procedure for Valve's Steam client, but completely unnecessary for Gog's version.

That is a good point. I remember that I did use the Steam client to uninstall the game first, before installing it under GOG. With regards to the registry part, I don't think i have cleaned it up during that time, though I assume that when I use CCleaner (3rd party app) it should do the trick as well.

Anything that I should be aware about? I could try uninstalling from the GOG client, and do another thorough clean-up before reinstalling it again....

Wait, tying a network login setting to the registry and not in-game coding is standard for Valve?! Why would you do that?! The risk of this exact problem, of a bad uninstall ruining future versions, is a reason you don't put lockouts in registry files