If you've installed certain addons (either via Steam workshop or downloaded from web), when you host a local server on L4D1 maps (namely: The Sacrifice, Dead Air, etc), after a new level is loaded (usually the 2nd level), your game will crash to desktop with the error message ".
Recently I returned to L4D2 to play with friends who just got the game during Christmas giveaway, it is still a nice experience, abeit some newly found bugs, like the "Model not precached" CTD errors while hosting local server on L4D1 maps, however I've figured how to fix them, here it is: I don't have this game on my disk atm but I'll let you guys know if there's a workaround asap, *sigh in Hunter growls*.
As of September 2020, this guide is probably no longer applicable due to the new update.