I'm currently working on my game with the gui editor trying to use the "Lock Exit" block in the script for "After leaving the room", however, when I use the drop down menu on the block no exits appear, rather a blank white drop down menu. My game is currently in the early stages and only has 4 exits at the moment. I've also tried using the "Lock Exit" block in the "After entering the room" script but I get the same outcome. Any help on why this might be happening would be appreciated.

To use "Lock Exit", you need to look in the object tree on the left hand side of the screen and select the exit you want to lock.
So for example 'room1' will have 'Exit: room2'. On the new screen that appears will be 3 checkboxes. "visible", "scenery" and "locked". Check the locked box, you can now give the exit a name which you use in a script to either 'lock' or 'unlock' the exit.

The dropdowns for exits only list exits that have names. Just go to the exit and put something in the "name" box, so that you know which exit you're selecting.

Thank you for the solution, I wasn't considering the fact that the name had any part to do with it.