That sounds like the demo save file problem.
If you previously played the demo then it left a save file on your computer.
And when you start the full game it tries to load that save file.
But after the demo was made, achievements were added to the game.
So when you start, at 98% it tries to load achievement data from the save, but that doesn't exist, so it fails.
The solution is to delete the save file, then the game will make a correct one when you start the first time.