So i was trying to raid a planet when this happens to me for the first time ever. I have way more deut then needed for the trip and the cargo is obviously departing empty, so why am i getting an error message that says im low in deut and with a negative cargo space?

It means the trip takes more deut than your ships can hold. Send an SC along with it and you'll be fine

ah, ok, thanks!

or you can just slow it down to like 70 or 80% as well. If you are not in a crunch for time

Thats the point of sc, it slows it down too