The global file is created by the game when you make a save. It stores the information for the preview of each save slot. 

If you can't save in general, than your game might be on a write-protected (="Read-only") location on your system. Try to move the game folder somewhere else or change the folder permissions to change that.

If you want to copy saves from an older version into the folder of a new version, but you're missing the global file, create new saves in the new game version in each save slot where you previously had saves, and then overwrite the newly created save files with your old saves. (The preview will be wrong until you load and save in those slots again, but the content of the saves will be your original progress.)