The map stopped launching in the map editor. (Again.)

500 MB? This poor game, with a map of only 40 MB, starts crashing every other time you try to load a save. It definitely needs to have most of the files moved into a separate .pak file and stored in the data folder. The "read-only" checkbox can be unchecked by right-clicking on the archive, opening "properties," and looking at the bottom of the window that appears.