Cannot play multiplayer due to update issues?

My brother and I tried to play Sins today (the base game as he doesn't have the expansions yet), but we were unable to get it to work due to a great many reasons, but the main cause seemed to be updates not alligning.

First, I was using my new Steam version of the game, while he was using the one from impulse (now gamestop) which he installed immediately before playing, when we received game data issues we tried playing over LAN and ICO, but the issues appeared everywhere.

So, I loaded up my older impulse (gamestop) version and updated it to the newest version (1.193.078 I believe), but that still would not let us connect. We could still both get on ICO, but the games wouldn't connect. We also tried LAN and nothing flew.

So, we both uninstalled fully and redownloaded the game from Gamestop and even that didn't work. What did I do wrong?

No, neither of us are using Mods or anything. I can't think of any better way to guarantee that our versions are identical than to have both of us download the same game from the same place at the same time.

Help! Alternatively, does Steam to Steam versions work better than this stupid Gamestop one? I don't like that app at all, especially since it pinned itself to my Windows Taskbar, as if it matters that much to me.