This works fine for me, I just tested it with the latest version, no problems loading it. As such I'm wondering if it's an issue with your game PAK files (or you selected the wrong directory for your game data). Try to use the PAK tab to open main.pak and textures.pak and see if you can successfully extract a file (right click to extract).
Yeah, you're right!
The file textures_1.pak is corrupted it seems. The thing is... can one mod that put some files in "public" folder, corrupt textures_1.pak? Maybe when the game is loading textures it modify the textures.pak in order to add them.
Well, I will do a clean installation of the game and try again, hope it works.
PD: I don't know what I've done but now works. I reinstalled the game in another directory but still can't open correctly the .pak (textures_1 and textures_2), so I renamed to .paka (don't matter) and the save editor could open THE SAVE correctly (the -pak still seems corrupted). So I renamed again and... now it works with correct filename! xD (still seems corrupted .pak)
I have just edited the savegame and works perfect! (well, one game-crash because I add some weird values to an item).