Well here i will help you solve the problem that doesn't let you load a map and gives the error could not read fastfile for zm_...
1-It is simple , first go to the folder where you have installed black ops 3
2-Select usermaps ( it is the folder with all your custom maps)
Here are some maps i think all of us would like to play
Steam Workshop :: GULAG ZOMBIES - Remastered
2-TMNT ZOMBIES! V: 1.11
Steam Workshop :: TMNT ZOMBIES! V: 1.11
Steam Workshop :: Ah-Peku
4-Agartha's Revenge (WIP)
Steam Workshop :: Agartha's Revenge (WIP)...