First off, my apologies.
Quite a number of bugs and glitches were reported the day before release and I made several patches to make sure the game was up and running smoothly for release, this, however, caused the old save files to corrupt due to new code being added to the game.
I have a solution to the problem but it will resort to having to play an older build of the game most likely riddled with some bugs and glitches.
To access the older build you will have to access the game's settings via steam (properties) then head over to the (betas) tab. You will find the save fix build there, If this does not work for you then it may be another build riddled in the mass amounts of updates.
Again, I apologize deeply but I wanted to make sure that the game was bug and glitch-free for its initial release.