Just to be clear. You are not trying to load older save games? Saves made before the RoI update is unsupported (because of the map changes among other things)?
I have been creating a few games and I am able to load them no problem.
If you are still having problem with creating new saves. Try the following:
1. Verify integrity of game cache through Steam
2. Delete the "Crusader Kings 2" folder under "My Documents/Paradox Interactive" (make sure to save you save games someplace else if you want to keep them)
If problem still persists:
3. Do a clean re-install of Crusader Kings 2
If you are still having problems after that. How are you saving the game? Locally or on the cloud? If locally, are you compressing your save games using the new check box in the save menu?
Would you be able to upload a save game with this problem? That way, I may have a look at it and see if it works on our end.
And also, are you using Windows, Linux or Mac (if it should be a platform specific problem)?