Originally Posted by master zionosis
This seems to be the most common bug that occurs, I'm not sure why it happens but just do what Mindtwistah said and remove your Override folder for the Spacewalk.
It seems like there is one or a few mods that modify the trigger template used for the trigger in the Asteroid Exterior area to trigger Atton's talk and the scene where the ship arrives. Since the name of this UTT file is not unique it will override various triggers in multiple areas, breaking all but one of them since it no longer fires the correct script, if put in the override folder.
So, check your override folder for files with the .UTT extension and move them out of the override folder, and reload a savegame from before entering the Asteroid Exterior area and it should work. (Don't remember the exact name of the UTT file in question.)
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FindRefs is a very useful tool to ensure that the names of the files you want to modify are unique so your mod won't cause game breaking bugs. Unfortunately some modders don't check this before uploading their creations.