CS:S Can't spawn bots in custom map?

Hello, every time I try to spawn a bot in a custom map the line "No valid walkable seed positions. Cannot generate navigation mesh" comes up in the console.

I have tried moving the maps to the "maps" and also the "download" folder within cstrike. The .nav files are there for all of the maps too.

If anyone knows how to fix this please let me know! Thankyou!