NPC zombies without a nav mesh

i wanted to add NPC zombies to some maps on my gmod server. the problem is only like 3 maps i have the nav meshes needed to spawn the zombies.
i attempted to create a navmesh using “nav_generate” and it makes the .nav file for the map.
the problem is even after generating a .nav file i still have no nodes in the nav mesh when the server is restarted. the server created a .ain file in graphs folder but that file is pretty much empty.

for spawning the NPC i use Zombie/NPC Invasion (http://steamcommunity.com/sharedfiles/filedetails/?id=179517028)
i have tried creating a navmesh by hand with Nav Mesh Editor (http://steamcommunity.com/sharedfiles/filedetails/?id=148638160) but that still did not work.
i get my maps from the steam workshop so that might have something to do with it.

any ideas?

To generate the nav mesh you need to provide at least one walkable position using nav_mark_walkable or something like that ( search for it using autocomplete ), and THEN use nav_generate.

that did not work.