MMD Wars, lockers vs unlockers: a new chapter
Once failed the way to invalidate the PMX format changing the fourth character in the file header definition, too easy to solve the issue with tricking the files/folders permissions (read only, hidden, etc), it seems we have a new battlefront. PMX models with no "4th character bug", no weird r/w permissions, but still causing the infamous PMX Editor's load error message (by the way this is, once again, the umpteenth proof that no valid/legal "locking" is applied by "lockers" but an intentional file corruption in order to cause malfunctions to users).
A temporary fix: Load the model in Blender, using MMD tools plugin ( fav.me/dacqbvw
) then just export the model into a new one. The exported model is clean and can be normally handled in PMX Editor.
Consider this just as a temporary fix, as I've not given a deep (hexadecimal) look, but at a first sight it seems (comparing the invalidated file and the working one) that an unexpected block of appearently non-sense chinese characters has been added after the blocks containing the model's infos (name/title and description).
It would be interesting to investigate why PMX Editor fails in loading the model, while both MMD and Blender still work (I've not tested in MMM).