Dear n3dd,
Thank you for your feedback!
Basically, a lot of things has been changed between the Early Access and the Final release in Adam.
Your old save files probably points you to a location that moved around, or didn't exist anymore, or completely changed.
You can easily continue your progress in the game by replacing your old save files with new ones.
I have a discussion on Steam about this here:
https://steamcommunity.com/app/1121590/discussions/0/2568690592372331846/
Thank you again,
Adam.