Make sure that the mods are actually for the current version of Project Zomboid. You can easily tell by looking at the title of the threads and checking if the version number (for example [2.9.9.17]) matches the version you are playing. Some mods haven't been updated yet.
Besides that the current modloader of the Steam Interim Build 64 Bit has some issues with loading certain mods - this will be fixed in the upcoming release of PZ though :)