Before it crashed as soon as I'd click on the wall, the selection was a solid red instead of glowing red. I'm not entirely sure what this is, so help would be appreciated, and I can provide screenshots and such if need be.
It's a wall that hammer has flagged as an invalid solid, so if there's any way you can select that wall, delete it. Maybe stretching a box over the selection and take out whatever's in that area. Otherwise you could use the "check for problems" under "Map" to see if it can be fixed/deleted that way.
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