I've managed to script a terminal so that I can unlock then re-lock a door via a terminal. But after creating the script, when I try to open the door once it has been unlocked by the terminal, I get the message "this object is activated elsewhere".
What is the correct way to make a terminal unlock/lock a door?

That sounds like a problem with how your door is set up. It's likely your terminal is functioning just as you want.

If I remember correctly, some doors have a script that causes that message to appear when the player activates them directly. If this is the case, you'll want to use a different door - one that can be opened directly.

Cipscis

That message is usually only shown when you try to 'Activate' the door using the 'players' credetials.

1) What script do you have on the terminal option for locking and unlocking the door.
2) And what door Editor ID are you using?

The door I'm using is a "Vault101CellDoor". I'm using the scripts:

Is there a script on the door itself?

No, just on the terminal which is linked to the door.

Yes, that door "does" have a script on it that blocks the player from activating it.

If you want to use that door, make a copy of it and remove the script from your copy.

Thanks, it worked.