I've got two linked_portal_door entities in my map, with width of 768 and height of 1024. When I compile my map, the compiler doesn't show any errors. Even the Interlopers' error checker can't find anything out of the place. Linked_portal_doors have never ever crashed the game, but now Portal 2 just shuts down when the map is finished loading. I'm quite sure it's the linked_portal_door, because when I cordoned them out, the game didn't crash.

Update: It seems that the size of the linked_portal_doors does the crash. I change the size to 128x256 and it didn't crash.

Update 2: All right, I solved it! It seems that you have to input 1/4 of the real area the linked_portal_door covers. For example, you wanted to make a 768x1024 sized portal_door, you need to give the entity 1/4 of the real size, so the area you want to give to the portal_door is 384x512. That means you have to measure one corner of a rectangular area to get the value the portal_door wants. I think I explained it quite badly, so if anyone wants to confirm my theory or clarify it, please do.

Yep, world portals should be half the width and half the height of the area they cover, like a radius, but in rectangular terms.