In my latest update, which should be coming out soon after moderator approval, I have removed support for random 3rd party mods (from now on, only mods from BeamNG's official repository and 2FastRacing's official repository will be supported). This should help fix your issue. If not, please let me know.
It sounds like you are trying to spawn a config for a mod vehicle that you don't have enabled/installed. All configs for the default vehicles in BeamNG should spawn normally. If this isn't your issue, please DM and I will be happy to assist you further.