This is the only thing writen in the Lua.log when the game crash.
[6207.404] Initializing Lua 5.1.4
[6366.338] InstalledPanel: Refreshing Mods
[6366.338] InstalledPanel: GetModBrowserListings()
[6366.650] InstalledPanel: Refreshing Mods
[6366.650] InstalledPanel: GetModBrowserListings()
Hmm, well that's the lognotes for going in and out of the mods menu. I assume you tried to start a multiplayer game and it crashed immediately? Did it crash before you get to the lobby or after you click the start game button? Does your modpack use a custom dll?