i have not seen the Host_error: bad string error before, so i do not know how to fix it. sorry
well, i went and looked around, and this is what i found:
This rare error only happens in game/server mode when sprites, models, sounds, or text strings (but not all strings!) are initialized and precached. If the string/name for the sprite, model, sound, or miscellaneous text string either starts with a non-printable ASCII character, or is 0 length (ie: starts with a non-printable null ASCII character), then the error will occur.
Solution: search thru entities like env_glow, env_sprite, ambient_generic, env_shooter, etc. - anything the engine has to precache a file for the bad name.
i dont know if that makes any sense to you, but if it does, then you should consider its advice