Are these save games from this version 0.6 if they are from older versions that could be the reason
in my case, the save games are from 0.5 i actually had the same 'fix' as the last dude - re-unzipping the files, and saving it over the first lot of unzipped files.. then i was able to open the save games...
the save files are still from 0.5 (of course renpy saves are in the separate windows appdata folder, so they werent modified by this process) but are now working for me.
i just figured you'd like to know more about the issue, so i posted the log for your benefit.