If you are having L4D2 crashes because of population precached errors for common infected look for any of your campaigns that have population.txt files and disable the campaign in addons before you play. This population file will be inside the script folder of the vpk in your addons folder. For instance "The Hive" (a great campaign) has one and will cause issues if you aren't aware of it. Good news is you don't apparently have to uninstall the addon. Just disable it until you are ready to play it. If you find this to be incorrect let me know and I will amend this answer. This conversation was gleaned from a steam forum.