@Nuke615 I had loading errors before and just closed the dialog window, and then I could play normally after. Does the game close when you press OK?
If it doesn't, maybe it couldn't load some parts of the save; you could try to play and check if something is missing; then try to save what you want in the gallery and start a new game and place again to check what can be saved correctly.
As you had custom content, maybe the game is trying to load parts of it which could be remaining in the save file and it's not available or compatible with the game version anymore (so the saves may have became corrupted).