Make sure you're not trying to target a station, or any other non-planetary object. They are (genuinely) not a valid target because the Carriers appear to be only permitted to instance next to planetary bodies (eg orbit, or barycenter). So if you try to target anything not a stellar body, that can cause it. And it'd be unfortunate if you cashed the carrier for that reason.
Yeah, other objects don't have slots available for orbits, although you can target asteroid clusters but I suspect that uses stellar orbital slots available between the bodies anyway.
And yet, you can target an installation in development - surface or space - but the plotting seems to default to the planet or nearest large body.Yeah, other objects don't have slots available for orbits, although you can target asteroid clusters but I suspect that uses stellar orbital slots available between the bodies anyway.