Nav Mesh
In order for bots and hostages to work with a Counter-Strike: Source map, a navigation mesh file must be created. Until someone writes this up, refer here.
Introduction
A Navigation Mesh represents the "walkable areas" of a map. This data is used by CSBots and Hostages in Counter-Strike:Source, allowing them to "know" how to move around in the environment.
Navigation Mesh data is stored in a .nav file corresponding to the map file (.bsp) for which it is used. For example, the nav mesh for cstrike\maps\de_dust.bsp is stored in cstrike\maps\de_dust.nav.
To support the many community-created maps, Counter-Strike:Source includes an automatic mesh generation system. The first time you attempt to play a custom map with bots, the generation system will build a .nav file for that map. Depending on the size and complexity of the map, this may take a few minutes to a few hours. Most maps take about 5 minutes to auto-generate a .nav file. Once the generation is complete, a .nav file is saved to your hard drive for future use.