Exit only allows you to leave the current container (the cruiser) in to the next container (a ship or facility if the cruiser is docked or the planet if your on the ground of a planet). You do not open or close the docking port that is just the message you recieve if you are not docked or on a planet, when you can't exit as you'd be exiting into space, atmosphere or terrain you cannot travel on.Edited By: Ralgarrch on Year 10 Day 160 8:36
If you are at the same location as the freighter, neither the cruiser you are on nor the freighter you are trying to enter being docked, the right portion of the position screen when in the cruisers entrance room will show the freighter and there'll be an enter button instead of:
"There are no facilities, ships, space stations or vehicles that you may enter."
Enter will also appear as a menu option with 'Party' and 'Room' which will bring up the same information that is shown on the right anyway.
If neither of those are happening you are either not at the location of the freighter, not on the crewlist of the freighter or not assigned to the freighter. You don't need to be on the crewlist if your assigned but even if you own the freighter I believe you still need to be assigned to the freighter.