Whenever I try to host a multiplayer game, players without the GOG version of the game cannot play, because they crash when trying to join.
So, I research a bit, and my version is 1.2, when the latest stronghold crusader version is 1.1
Therefore, people without the GOG version of the game cannot play with people with the GOG version.
Is there a fix for this?

Best remedy is to use GameRanger to play multiplayer games.

Except that only helps people to connect to other people, it has nothing to do with the game itself crashing.

I'm getting this too. I enter my friend's IP while connected to Hamachi and it then turns up with the results for that ip. When I try to join, it freezes and then the game crashes to the desktop.

Running Vista Home Premium 64 bit, I am running the game in Windows Compatability Mode for XP SP2 and am running as admin.

I've seen other threads about this, I read that some router setting fixed it for one woman.

Have you tried disabling UPnP on your router? I think this might be what is causing the crashing. It usually causes problems with older multiplayer games.