That is strange that it works 1 time after reinstalling the editor.
The only 2 things I can see happening is
A) if it's been a while since you've edited the map, check to make sure your aigrid data is in the correct path. This was fixed last Friday though, so it's unlikely this is your issue.
B) remove your terrain files from your mod, should be in ..\data\mods\<yourmod>\<modlevel>\terrain with names like terrain_000, terrain_001 etc etc. Try moving these to a backup folder. I had this happen once and had crashed on loading my level. You might just need to recreate your terrain as the painting is stupid buggy right now (that's how mine came to be corrupted- any instance of painting I hold my breathe). Luckily, any objects and all that will still be placed.
I hope this helps, if not sorry bud.
