Many of the files in the the latest save are corrupt. That is why the zip is half the size of the other 2 saves, even though it contains extra files, added for the Black Ring dungeon. If you open the zip file in Windows Explorer, one of the columns in details view lists the compression ratio; getting 70-90% for large files in the save is normal, but 100% is not.
In particular, the data.000 file (which contains the character and all NPC data, as well as some quest information, etc) is entirely zeros, so the game can not read the save version, which triggers the warning about it being an old version.

The previous save is immediately before that point, though, so you can just continue from there.