When creating maps for Condition Zero make sure the CZero bots dont learn the map while it's still in development. (You can do this by NOT including bots to the game)
I noticed that I accidently included a cpu player - bot - into the game the first time i ran a test run, so they learned the map (as they do it automatically when its an unknown map). But because I added more stuff to the map, the nav file the bots created was quite incorrect, which resulted in this in this problem where bots don't join anymore and the hostages are stuck at their spawn locations.
I fixed it by just deleting the .nav file in the maps folder. (I figured out that this couldn't be a map error)
Example: my map is called cs_map1, which is store in (condition zeroczeromapscs_map1.bsp), and the .nav is stored in the same folder, with the same name as your map, in this case "cs_map1.nav"
So, if you ever have this problem (this is only for Condition Zero and CS:Source, not 1.6), just delete the .nav and don's include bots.